Have you tried the Shebeest SSS short? The chamois is a little softer/less dense than the Ultra D chamois, but it's quite similar.

Also, I would try the Terry Bella short if you haven't -- the chamois is quite similar to the Shebeest shorts.

You might try Castelli shorts too. Both the Kiss chamois and the chamois in their more expensive shorts are thinner than the Shebeest chamois, but like the Shebeest chamois they are flexible and not diaper-like. I find them to be more cushiony than the RS chamois too (I have a pair of RS shorts and my reaction to the chamois was similar to yours). The more expensive Castelli chamois is not thicker, but it is denser. Castellis are my favorites.