The Ultra ThinLine Sheepskin Comfort Half Pad was the answer. This pad features a beautiful sheepskin lining, the Ultra ThinLine up the upper side, and pockets where you can add ThinLine shims to further adjust the fit of your saddle. The pad itself is pretty thick, and gave the saddle just enough fill so that I didn't need to use additional shims.
I've been thoroughly impressed by this pad. The sheepskin is soft and makes for a comfortable ride when placed directly against a horse's coat. I've been using this pad with a baby pad to help reduce the number of washings that I have to do. Having used this pad for about four months now, it's held up beautifully and the front and back sheepskin rolls beautifully frame by saddle.
There's a noticeable difference in comfort when I use this pad versus other half pads, which I attribute to the ThinLine material. ThinLine technology features excellent shock absorption properties, absorbing much of the impact that occurs during a ride. This makes for increased comfort for your horse's back, while also providing a more comfortable ride for the rider.
Whisper seems quite content when I ride with this pad, and I can attest to the fact that I feel less of a jolt on my back at the trot and canter. I have pretty consistent back pain, and this saddle pad absolutely makes a difference.
I like the fact that this pad is customizable so that you can find the fit that works best for your horse and saddle. Each side of the pad has a pocket for a front and a back shim, so you can raise the front, back, or both sections of your pad. This is a great solution for saddles which are just a little bit too wide or slightly unbalanced.
The Ultra ThinLine Sheepskin Comfort Half Pad is available from ThinLine for $259. While the price is a little steep, I do feel that this pad is worth the money.