Help need saddle to fit massively overweight 13hh highland pony!!!

We have just got a 13h highland pony on loan for my little brother and she has been at grass for 12 months and is majorly overweight with a big crest on her neck and alot of weight around her should area where the saddle fits. We have tried every kind of saddle we can get our hands on even full size eventing and jumping saddles for horses of 16hh and still can't get anything to fit. The problem is the bit of the saddle that should fit on the withers is being pushed up and tipping the saddle baack because of the weight around her shoulders. I am lunging her 3 times a week and walking her once a week and the weight is coming off slowly but my brother is getting fed up and losing interest as he can't ride her as she is too fat to stay on bareback any ideas for saddles would be appreciated!

The thorogood cob is quite a nice wide fitting saddle, and not too big everywhere else, otherwise, you could try treeless.

Try a treeless! There are some pretty nice looking ones these days so you don't have to worry about it looking a bit...wierd!

Failing that, try a racing saddle. There's a horse at my college, she's built like a tank & her shoulders are absoloutely HUGE & she's had both a racing saddle & treeless saddle & both fit like a glove :)

I was thinking treeless would best, then it will still fit if the horse loses weight.