LOL, can't really help with that one Turndial, when I first went horse shopping as a re rider, I was a lot heavier and a lot older than you. I decided after a lot of research that a Haflinger (hey you have them in the UK as well) would suit me fine, small enough to get on, small enough to fall off.
I found my beautiful stout little Haflinger, she is easy to get on, if you use a block, the first time I sat in her I just felt so odd, and scared, and figured it was because I was older and fatter. Over time though I've discovered that while I love her deeply, and I think she is the prettiest girl ever, I HATE riding her
My mount for the last couple of years, has been a 15.2 hh appyxdraft, need a mounting block to get on, but a bonus is he has withers to anchor the saddle, I feel far more secure in him than I ever did on her.
Last year I started riding my 16hh rescue very drafty mare and that was even better, and now I have a verging on 17hh horse outside ready for me to try.
After all that, my advice, go and ride as many different types, heights and shapes of horses that you can, and find the one that makes you smile.