The ones that connect to doors or ceilings usually have a weight limit of 200 pounds. There is also a product here, the "Universal sex swing stand", to which you can connect the sex swing and has a weight limit of 400 pounds. In general, for any kind of suspension play, it's considered safer to use a metal stand or other contraption that is weight tested for a minimum of 400 pounds to affix the restraints.
The only other concern would be comfort: If these products are not used properly, they can be uncomfortable to wear and can cut off circulation, which is also dangerous. I am a "thick girl", too, so this is usually the major sticking point for me, as well.
Hope this helps. :3