Yeah, Pete's pissing method might not work for you... It involves sitting on the seat with your knees, facing backwards, and then dropping the waders. Probably not good for a feeble old man like yourself :-) What size wetsuit do you have right now? I've got a two piece 3.5mm that I use for scuba diving. It stays nice and toasty, but of course on my torso I've got 7mm, and 3.5mm on my legs and arms. 3.5mm all over might get a little chilly, but I'm usually hot in that suit. A 7mm farmer john wetsuit should be just fine.
-Brian