Definitely an Ogilvy! I have one and I love it more than anything else! Plus it's super fun to customize and match with😏
I would definetly recommend an ogilvy pad. they fit very nicely on all horses and provide lots of support for horses with sensitive backs. In my opinion they are a little bit more on the pricy side but are definetly well worth it.
Passier flexipads are really good! http://www.passier.com/en/accessories/saddle-pads/flexipadr-dressage/ or http://www.passier.com/en/accessories/saddle-pads/flexipadr-jumping/
For me the most important thing is that the saddle fits correctly. If this is the case then I don't think the saddle pad matters a lot, but a half pad (pad between saddle and big saddle pad) can make a huge difference for your horse. For me it is really important that the half pad does not change the fit of the saddle. For my horse with a very sensitive back I really like the Ogilvy memory foam half pad. It is super shock absorbing and I have noticed a huge difference since i started using it. Unfortunately it also quite expensive, because you pay for the quality :) Another half pad that I use quite a lot is one with sheep skin on the inside, for my idea this just provides a little extra soft layer between the saddle and the horses back, and all 3 of my horses also go really well in this. Hope this helps :)