hi there, what style are you after
old school >89 - might feel funny as geometry was design for small kids, but loads of big riders are fine with them
mid school >00 - some built like tanks and weight the same - harder ridden - haro look sweet
old new school >06 - mass production - choose from known company - mongoose and GT
new school >12 - loads out there but prices are high even for a standard one - what out for cheap copy style stuff - it will brake and hurt
there are loads of good bikes out there and for >£100 you will get some thing good - but it depends on what you are looking in to getting - weather it's clean or you need to do some work to it
do you homework on what you need / like / and will be best for you
put any links up on here that you spot and we will see if good or not - don't forget that loads of people look on here and if you have just flagged a bmx that they also like, they might get it instead - you might not get the one you see, as some slip passed
ask any questions you need - you say your bigger, i have seen some big guys float like a butterfly and sting like a bee - it will feel small and different but it will help your MTB riding - it might even make you change to a real bike and leave the easy mtb at home
hope this helps a bit - cheers B