Sounds like you need a very lightweight combination.
I had a very cheap and extremely lightweight (300g) Hanimex 300mm f5.6 mirror purchased in the very early 1980's.
https://lens-db.com/hanimex-300mm-f56-mirror/
It used a T ring adaptor. The correction was surprisingly good across the field on the example I owned which I discovered on those rare occasions I could fluke the focus right. In the film era, focusing was a challenge. I didn't have a knife edge focuser. Focus is not a problem with modern DSLR's and live view or an astrocam.
I can't vouch for how they would perform with a digital sensor. Keep in mind that film grain was 5-10 times bigger than pixels found in modern digital sensors.
They are no longer in production. If you could find a second hand version it might do the job.
There is one on eBay here:
https://www.ebay.com.au/itm/20479712...Bk9SR-7JtOaSZA
Joe