Newbie questions

Hi guys, long time lurker, first time poster.
I've just come back from a weekend surfing. I've only had about 15 hour to 2-hour sessions so far in my surfing life spread over a year and a half. I'm a big bloke - 6'5" tall and 16 stones (220 lbs, 100 kilos). I've been snowboarding for years (not that it's helping me much at present!) so I've got decent balance.
I started off on small swells and 9ft+ longboards (foamies) but earlier this year moved to an 8'4" mal. I can catch (almost) every wave I go for, and on the 8'4" was standing up on most of them (I have to work on my pop-up, I still half-kneel sometimes) but this was on quite small, mellow waves.
This weekend was fairly large (to me!) and messy at 5ft. Therefore hired a 7'6" mal on the advice of the shop (22 3/4 wide, 2 3/4 deep) and didn't have too much trouble catching waves again, but was finding it much harder to stand - the board was far twitchier than the big planks I'm used to! I guess that's just going to take time to learn to use, right?
Anyhow, I found that it was tough to get out as the waves were pretty big and there was a lot of powerful whitewater or even breaking waves crashing into me on the way out. Ended up in the no-mans land in chin deep water just holding station and either trying for a big white-water just-broken wave or the occasional smaller wave that came through. If I went out a bit further, I found it tough to get stabilised in the water due to the continuous pounding of the big waves. I guess I could have made it out back if I'd presisted during a flatter spell, but didn't feel confident about what I could do once out there.
I find that if I catch the whitewater, no matter how hard I paddle, the backwash holds me in place, the wave slaps me hard and I just try and get up in messy white water. If I occasionally get a cleaner wave, I get that exhilarating accelaration as the board slides down the wave but I always struggle to know when I've caught the wave and end up trying to stand up when I've already gone 10 feet ahead of the wave... this leads to losing speed and sinking!
I suppose it's a case of either being incredibly lucky with the swell so it's just right for me, or I just have to bite the bullet and go out where the waves are cleaner and learn to get up as the board picks up speed? Seems very scary - the prospect of going out where the big waves are crashing in. Especially on a small, twitchy board! I have a friend who is only 5'10" tall and he has a 6'8" shortboard. I pointed out to him that my 7'6" is the equivalent of a shortbaord to me! I don't know whether I should go bigger or persist with learning on the slightly shorter board... In the long term, I suppose sticking with the shorter board will help me more?
Is the only way forward to go out where the waves are clean, stay clear of the mushy white water and learn to pop up earlier? I've kind of had enough of the "stand in chest deep water and get clobbered by wall after wall of white water" thing, to be honest!
I've just come back from a weekend surfing. I've only had about 15 hour to 2-hour sessions so far in my surfing life spread over a year and a half. I'm a big bloke - 6'5" tall and 16 stones (220 lbs, 100 kilos). I've been snowboarding for years (not that it's helping me much at present!) so I've got decent balance.
I started off on small swells and 9ft+ longboards (foamies) but earlier this year moved to an 8'4" mal. I can catch (almost) every wave I go for, and on the 8'4" was standing up on most of them (I have to work on my pop-up, I still half-kneel sometimes) but this was on quite small, mellow waves.
This weekend was fairly large (to me!) and messy at 5ft. Therefore hired a 7'6" mal on the advice of the shop (22 3/4 wide, 2 3/4 deep) and didn't have too much trouble catching waves again, but was finding it much harder to stand - the board was far twitchier than the big planks I'm used to! I guess that's just going to take time to learn to use, right?
Anyhow, I found that it was tough to get out as the waves were pretty big and there was a lot of powerful whitewater or even breaking waves crashing into me on the way out. Ended up in the no-mans land in chin deep water just holding station and either trying for a big white-water just-broken wave or the occasional smaller wave that came through. If I went out a bit further, I found it tough to get stabilised in the water due to the continuous pounding of the big waves. I guess I could have made it out back if I'd presisted during a flatter spell, but didn't feel confident about what I could do once out there.
I find that if I catch the whitewater, no matter how hard I paddle, the backwash holds me in place, the wave slaps me hard and I just try and get up in messy white water. If I occasionally get a cleaner wave, I get that exhilarating accelaration as the board slides down the wave but I always struggle to know when I've caught the wave and end up trying to stand up when I've already gone 10 feet ahead of the wave... this leads to losing speed and sinking!
I suppose it's a case of either being incredibly lucky with the swell so it's just right for me, or I just have to bite the bullet and go out where the waves are cleaner and learn to get up as the board picks up speed? Seems very scary - the prospect of going out where the big waves are crashing in. Especially on a small, twitchy board! I have a friend who is only 5'10" tall and he has a 6'8" shortboard. I pointed out to him that my 7'6" is the equivalent of a shortbaord to me! I don't know whether I should go bigger or persist with learning on the slightly shorter board... In the long term, I suppose sticking with the shorter board will help me more?
Is the only way forward to go out where the waves are clean, stay clear of the mushy white water and learn to pop up earlier? I've kind of had enough of the "stand in chest deep water and get clobbered by wall after wall of white water" thing, to be honest!