My 4yo has outgrown my 7" gullet saddle. His shoulders are very wide and pronounced and he has a bit of a dip behind them. He's getting wider but not filled out yet. I tried on several saddles with my trainer, both English and western, and nothing worked. I'm at a loss for what to try next and I'm on a tight budget.

Are you asking what pad you could use with your saddle that your horse has outgrown?

If so, the answer is NONE. If the saddle is too small, there is nothing you can put under the saddle that will remedy that.

Personally, I've had real success with the Flex2 saddles by Circle Y. Yeah, their leather quality is not what it used to be, but the FIT of the saddles is just fantastic. For the last like 8 years, that's all I've used on 5 different horses and it's been great. However, I personally use the Lisa Lockhart / Badlands / Sarah Rose version. (It's all the same tree ... has just changed names).  For example, the Kelly Kaminski fits different than that one, which I tried one time and I didn't really like at much for fit.  

All of my horses have used the regular tree with the exception of one that uses the wide.

You might be able to find a used one in your budget?

What saddle brands did your trainer try? (western and English)

My Tad Coffin A5 jumping saddle has done quite well on most horses. It's not always a perfect fit, might be a hair wide, but it doesn't pinch and I CAN use appropriate English padding with it to fill in where needed, and I've successfully used it on a few different horses as well.