Would you not feel happier yourself riding something bigger? As has been said before, in this country (GB) people of 11stone and more do not ride 12.2hh ponies - that's not very kind. I too think it's best you try a native pony of around 14hh/14.2hh. A Fell (around 14hh) Dales or Highland would be the mount for you. If the pony sags when you're on it, then it's uncomfortable and, you wont be doing its back any good. So please, think of the pony and ride something a bit larger. I know you probably like to ride but the animal has to be considered and put before your fondness for small pony riding. You'll feel more comfortable as well.