I bought a treeless saddle at the recommendation of my farrier (who is no lightweight himself.) He uses them on some of his horses. I've been using mine on Dancer, though admittedly our sessions are pretty short - only about 15 - 20 minutes max. Daughter rides her a lot longer, but daughter is a tiny thing.
Now I hear that heavy riders should never use a treeless saddle because they don't distribute the weight of the rider. Is this true? Could I still use it for my short sessions? Dancer doesn't seem to be having any soreness issues.
We are working on building up the muscles on her topline. She's never really had a lot of muscle anywhere - when we got her she was really fat - but not well muscled at all. Carrying and nursing a foal pulled the fat off of her and she really looked bad. Still doesn't look very good, but she's better than she was. I don't expect her to carry me any great distance any time soon - she's not ready for that, yet.
I sure would appreciate your input. If I need to get a different saddle, I can sell the one I have and get a more appropriate one. She's just been hard to fit (I thought) but we used a regular saddle on her at the trainer's that fit quite well, and I could get one like that (larger seat size) without breaking the bank.