Well, I think it really depends how much padding you need and you will probably have to play around with different options to get the right fit. I have a Mattess Pad, Equine Comforts pad and a Wither Relief Pad by Total Saddle Fit. I love my Wither relief Pad by Total Saddle Fit (they make other half pads too). I use this with my dressage saddle. I am not sure what the material is for the shims. Whatever it is, it works and has been working for the past 6 months. When i was using my Mattess pad, which i don’t anymore, I used the felt pads provided and I also used a thin cut from a yoga mat. I would cut out the shape of the shims. The Mattes pad for me I feel is too bulky and it actually rubbed my guys withers. This is why I have the wither relief half pad now by Total Saddle Fit. I also have a ECP pad that I use the foam shims provided and 1 cut out of a yoga mat shim. I use this pad with my jumping saddle.
Hands down have been really happy with the look and fit of the Wither Relief half pad by Total Saddle Fit. I’ve actually thought about getting one for my jumping saddle.
Edited to add: I do like the ThinLine shims, they just didn’t fit my ECP or Mattess pad at the time. I will agree too with what other said, the foam shims are Junk for the most part. Depending how much padding you need of course.
It’s really all trial and error…