The main issues is how committed you are and do you want to make a 2 step transition to shortboarding (easier, more fun, maybe take longer, more expensive) or a one step (harder, frustrating, cheaper, maybe quicker). So from easiest to hardest, you would transition to: a mini mal, a 'thinner' performance style minimal and then, lastly, a shorter hybrid/egg/fish style board.
For example, if you got a minimal I reckon you could go 7ft4 or 7ft2 no problem.
I dropped from a 9ft2 to a 7ft4 minimal with nervousness (although I was 'pretty good' on the longboard), caught the first wave no problem and immediately realised I could have gone shorter. That said, it did take a while to get my wave positioning right, but actually popping up and riding the board was no problem.
The egg or hybrid boards much over 7ft dont really grab me too much, I think they are much better under 7ft. Dont know why, but if they are too big then I'm not convinced their outline works very well (maybe putting it another way, for bigger boards the straight outline of the mal shape just seems preferable. But I may be biased!)
So I would go
- (easiest) minimal low 7ft; or
- (bit harder) thinner minimal style, such as this type of board - maybe 7ft4 - you can see straight outline (the sides are straight) but a narrower nose and overall width compared to a mini mal. Probably needs bigger waves though
http://www.mctavish.com.au/surfboard/carveror (hardest transition): take the plunge and get an egg/fish around 6ft10 eg
http://www.surfindustries.com/surfboard ... h-3-pe.php http://www.firewiresurfboards.com/surfb ... =dominator http://www.markrichardssurfboards.com/b ... saucer.phpAll boards are just 'for information' - for sure there are probably better boards or boards you can actually buy where you live. They were just ones I pulled from easily accessible websites and most makers/shaper will have something similar in their lineup.
Obviously the harder the transition the closer you are to getting shortboard skills. If (a) you are committed to shortboarding and (b) you surf frequently (and (c) dont mind a bit of frustration), I would suggest go to a surf shop and demo an egg/hybrid style board for a session and see if you are totally overwhelmed or think it might be a goer.
Because, in reality, if you get a mini mal now your next board will probably be a 6ft8 or so egg/hybrid anyway. Can you make the jump to that length right away - potentially not; but maybe. Its up to you, I didnt - I went for the interim mini mal step and quite happy I did, because I prefer to enjoy my surfing and have no desire to become a shortboarder - but I'm old and lazy.
Then after the egg/hybrid move to 6ft4 or so - this will actually be the difficult move because the difference between a higher volume wider board like a mini mal or egg and a proper shortboard is much bigger than just dropping length.
Then see how it goes...