You might be surprised to learn which pony and horse breeds can carry the most weight! Most ponies are better suited for weight carrying than many adult horses. And draft horses cannot carry weight as comfortably as most stock type horses.
If you are a heavy rider looking for your next mount, resist the temptation to look for a draft-cross horse or a horse especially large to carry the most weight. Draft horses are built to pull, not carry. Calculate that the average horse can carry 20%-25% of their weight, and a well conformed, stout, and healthy horse may be able to carry and additional 5%-10% more comfortably. You’ll want a vet to examine your potential purchase evaluate conformation. A horse that is conformed well and proportionally will be able to carry more weight without adverse affects on their body.
Specific breeds to look for might be Foundation Quarter Horses, Stock Type crosses, Halflingers, Orlov Trotter, Bashkir Curly, Mustang, or stout Morgan. Aged 5-15.
Horseback riding is an activity that should include everyone and is a great way to stay active, but a heavier rider always has the responsibility to take care of their horse. A heavy rider has an obligation to ride well. 250lbs of wobbling rider can feel like a mountain to a horse, while a 250lb rider who is balanced, centered, and riding well can require less effort of their horse than a thin, poor rider. If you feel your balance on horseback is compromised, do yourself and your horse a favor and enroll in riding lessons for the sake of yourself and your mount!