If you are a heavy rider looking for your next mount, resist the temptation to look for a draft-cross as they are not the type that can carry the most weight for its size. 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.