C172 may still be tight for you, with instructor. I don't have the POH for W&B and max seat weight, but make sure you ask the nearby flight schools, too.
No point going through the hassle of medicals if the schools would not be happy to take you on or able to provide suitable aircraft.
I have partial empathy for you. I'm 200 or bit below, lbs and I'd ideally be below 170 due to R22 max gross limitations, for instructing job, not being limited to students etc. It's not easy to lose more than 10lbs in my case. Not limiting me from flying, but has an impact on my career start options.. Not nice feeling.
If we are faced with hard decisions, we can put high amount of energy into our actions. Losing weight could be one of those. We all understand the desire and passion for flying, aviation.
Hope it somehow works out for you. If not for regular aircraft, check out weight shift control/hangglider trikes. Lots of fun, too.