Are you familiar with the parallelogram mounts? Bintel have them, but they're not cheap (they go on an AZ-3 tripod, I think).
https://www.bintelshop.com.au/Images/Stock/6624.jpg
If you're rich and lazy, then you can buy one from Bintel (I think they have them in stock). If you're poor, handy, not lazy, and quite clever, then you can perhaps figure out how to make one yourself. If you're poor, handy, not lazy, but perhaps not quite clever enough, I think that there are a couple of places on the net that'll sell you the plans.
There is also another alternative. It's called the sky window or sky mirror, I think, which means you are looking down into a mounted mirror (much easier on the neck). Meant to be quite comfortable, but I've never used one. Also a bit ex-y, I suspect, for what they are, but perhaps capable of being copied in a workshop. (You'll find it mentioned somewhere in Cloudy Nights.)
Good luck,
Brian.