there are a lot of bikes around £900,try tartybikes,they can help you.it's not harder to control a 24 bike like "oh my god I can't do this",it's harder like you have to struggle a little bit(I for one like to struggle a bit).since you rode a bmx and you want bmx tricks as well,a 24" would be better(my opinion).keep in mind that a 24" is somewhere between a BMX and a 26".so you can do all the tricks that you do on a bmx, plus trials.your choice.
good luck!