Surfing Waves

hey guys, sorry for another "what board to buy" thread, i had a loook at some of the others and the general message i get is its better to learn on a softboard or fun board. so heres the story, i live in leicester (in the middle of england, nowhere near the bloody sea) and i go down to newquay and surf for a week every year, ive been going for about 4 years now, so id say 4 weeks of solid surfing. i had instructors for the first two times and they said i was progressing very well and showed some good natural ability. the last two times ive been trying different things and trying to progress on my own with my dad to help me, the last time i went i surfed on a 6"2 shortboard and got on nicely with it (baring in mind that i am 5"4 in height and no im not a midget, im 15)and the standard im at now is i can surf the unbroken face of the wave consistantly and getting some nice rides. i obviously want to progress further now and the way i see it is to get onto a smaller shortboard suited to my size and weight and start trying to get some nifty turns down, i would also like to get "out back" and try some of the bigger waves and see whats going on with them, obviously with a board that is pretty big for me i cant duckdive with that and get out there. so my first question would be, is there anything more i can do to inprove my surfing on the board im already on? and the second question being, if the first answer is no then what size board should i be looking at bearing in mind that im 5"4 and roughly 7 stone 5?

thanks guys, i apreciate that my little article is a pretty heavy read but i would appreciate help