[Waldbaer]

I am using this stand fro K&M with my Surface Pro 6 (should work with Pro 8 as well) and I'm very happy with it and had no problem with buttons so far.

K&M 19742 – Thomann United States (thomannmusic.com)

This works, of course, but it needs me to always take it with me (if you add the stand itself, it's quite stable but also big & and heavy) and won't hold any paper sheets or other things. If you want to handover your tablet to somebody else, he or she needs a special tablet stand, too or take the whole big thing with it... too many downsides for me. 

I just got a case from MOKO. It's big and ... bulky (not to say ugly), but it does the job. First quality impression is OK and it's not very expensive, too. And maybe it will also protect the Surface if it may try to fly... 
https://www.ebay.com/itm/203746274904
https://www.amazon.com/dp/B09MN8XPNB/
...on Amazon there are even several reviewers who had the same problem as we had here (portrait mode pushing buttons).