^ This would be my suggestion, basically.



A few years back, I was much heavier, had strength issues, and had problems getting the legs over the saddle (old injuries). Got a lower-step bike with some strength in the frame, in 26" wheel format, and promptly installed the fattest, strongest tires and tubes I could find that would fit well (26x1.9, IIRC). Wasn't sexy, but it worked well. Stayed with this bike until my strength and control was back to normal, more or less. Then, headed into the 700c/commuter type platform, which I'm on now. Still have larger (28x1.75) tires on stout rims, though (now) more out of concern for the potholed commutes than anything.

I'd suggest finding a late-80s or early-90s Specialized RockHopper or StumpJumper (or similar), then getting a well-made set of stout 26" rimes and strong hubs, then mount a great pair of puncture-resistant tires and tubes. With the right tires, it needn't have much drag or be that slow. With a great saddle that fits and a stem/bar combination providing great fore-aft balance, it'll also be far more comfortable. It'll be a tougher-duty platform than most 700c hybrids or road bikes, probably much more suited to a larger person. Might even be less likely to be stolen, if the vintage paint job is left alone.

There's a M/19 StumpJumper on eBay right now for ~$300 with free shipping, as an example. And there's a 19" Bridgestone MB3 on eBay for $200 (plus shpg). Something similar might make sense, with solid wheels and the right fit.