I'd recommend a steel bike like a Surly Ogre, KM or Krampus. A Kona Unit or Unit X, a Kona Sutra, a SOMA frame or something like that. Coupled with a tough wheelset designed for utility eBikes (
https://www.dtswiss.com/en/wheels/wh...hu-1900-spline) you should be okay weight-wise. Most bikes are designed to carry 130-150 kgs (285-330 lbs or so) and actually often have published weight limits in their manuals, but that wheelset is designed to carry 180 kgs (396 lbs). That wheelset is $400-$500 if you get it online from Bike24 or one of the other big online retailers from Europe, but it will last and has easily replaced components. It's also about the cheapest price you will find a wheelset designed to carry 180 kg. Guys will tell you to have a tandem hub built up into a wheelset, but some of those tandem hubs alone can cost $500 or so, before spokes, rims and labor costs are factored in. Cromolly steel frames are really tough, but in many cases, when you're a bigger guy like we are (I am still big but I was huge), you are let down by the bike's wheels. Get those right and everything else sort of falls into place.
Oh, and look at the WTB Comfort as a saddle. There are also often some decent deals for wide, comfortable saddles on Chain Reaction Cycles; their house brand, Brand X, has one and they also have specials on other brands.