I'm 5ft 1in and weigh in the area of 10st, i've been browsing saddles and know my ned is 17" i've seen a pessoa which is this size and has a 26in seat, would that be to small or big for me????
17" is the size of the seat, so it will fit you if thats what you're used to. You need to find out the width of your horse, eg wide, medium wide etc. and work from there. Horses are all different shapes so just because the sizes are somewhere near right, it doesnt mean that the shape of the tree will be suitable.