Well, I seem to have missed out on this whole thing when it started but better late than never, I guess. Welcome to the forum WBC and in my honest opinion, there is no such thing as being too big to ride so long as you can get into the saddle under your own power. It is all about finding a horse that fits your size and riding ability. You may end up being more comfortable on a draft or draft cross horse just because they are a bit bigger, but they also tend to be more mellow than the smaller breeds. However, that being said, any decent sized QH or similar breed should be able to pack you wherever you wanted to go for as long as you wanted to ride. The breed you look into might also vary depending on which discipline you want to get involved with. Are you more interested in riding english or western or maybe both?
Also, I just wanted to add that so long as they are trained properly, a draft takes to riding as well as any other breed. This is my percheron gelding John that I started and rode a few times last year.
Though I will tell you that after a lifetime of riding horses that were usually shorter than 15 hands, sitting on something that is 18 hands was quite an eye opener LOL.
My husband is 6'4 and weighs around 200 lbs. That weight for a guy that tall - he is pretty thin! However, he rides a 15.2 hand draft cross. When he started riding him as a 3-4 year old, he was actually 14.3 - but so wide that he looked fine on him. Horse carries him with no problem.
I'm 5'9 but also about 200 lbs. A haflinger who is between 13.3 - 14 hands is my main riding horse and he can out-go all other horses on the trail.
A nice stocky horse takes up a lot of leg and as long as that stocky horse is fit - he would be able to carry you all day long.
There is a horse out there for you...don't worry!!! Look for a horse who has a short-ish back, and is large in bone...I don't think height guarentees strength, and QH's started out on the short end 14-14.3 hh, and they were bred to carry around cow poke around all day...