Nppl medical isn't as stringent as ppl. You need to be certified as fit to drive an hgv. Ask your GP.
I'm very heavy and I've flown all sorts. The biggest restriction in my experience is room. I used to fly with another lumpy bloke in a 152. Ok we never filled it above tabs and top of climb seemed a long way away but we did it. I've flown little skyrangers two up and they were fine too. I can give you a few stone.