I think I remember someone on here experimented with using pantyhose or human socks under hoof boots (I use Scoot Boots) to stop rubs.
@Hondo , maybe that was you?
My mare had scratches on a hind pastern this spring. It's not cracked or scabby any more, but I miscalculated and rode her in hoof boots too soon into the healing process, and now we have some small rubbed spots with no hair growing in. I have padded gaiters on the back of the boots, and have been putting a layer of vet wrap around the hoof/heel bulbs/pastern that has stopped the rubbed out spots from getting any worse. But it's a bit clunky to wrap every time. I tried riding without the vet wrap yesterday, and she seemed a little sensitive on that leg when I took the boot off, so I think the vet wrap is providing some protection of the sensitive area.
I'm wondering how either of those options would stay in place without riding up when the boot goes on though. With the vet wrap, I go under the hoof so that it stays in place and doesn't end up bunching and rubbing even worse when riding.
I know a lady who has been doing novice rides here (10-15 miles) with Cavallo comfort socks under her boots. She's been doing pretty well so I don't think she's having any issues with them! Plus they're not horribly spendy to try.....