Well I'm not really one to talk since I'm 4'11 and barely 85 pounds, but I think as long as the horse doesnt seem to be under any strain and has a good back, you'll be absolutely fine on a 13-14hh pony- especially a welsh! Man those things are STURDY. And because of their naturally wide girth, you're legs probably won't look overly long ^_^ Like everyones been saying, the 'if your feet are under the girth, you're too tall' theory isn't completely true. Some horses are really narrow! Take these guys for example.
This is a friend of mine who weighs about 135 pounds and is 5'8, and she's riding a dales pony who is 13.2 hands at the very most xD granted, she is in an english saddle so her legs probably ARE longer than at his girth line, and she looks slightly funny on him, but he is obviously VERY capable of carrying her =] they trail ride for miles on end without him even hinting at becoming tired.
And then we look at 4'11"/85 pound me riding a morgan mare of the same height, but WAY different girth size (shes a very narrow build girl ^_^)- and I also seem to fit her snugly. You wouldnt be able to tell that there is a NINE INCH difference between slinky(the girl's nickname) and I when comparing photos.
So just opt for a 'rounder' horse- (a welsh would be absolutely perfect) and you'll look absolutely fine =] don't worry about it!
I used to freak out about weighing too much (180lbs) and riding a 1600lbs belgian x percheron. I leased her when I started riding again and she gave me the confidence to feel not too fat for my 1100lbs mustang:)