You should consider a portable work bench, either the Husky one or the Keter one:
https://www.homedepot.com/p/Husky-1-8-ft-x-3-ft-Portable-Jobsite-Workbench-224317/205887786

https://www.amazon.com/Keter-Adjustable-Workbench-Sawhorse-Capacity/dp/B00JU6SFP2

The Keter one may be better since it can be height-adjusted. These should work especially well for you because they would fold up, making it much easier to transport up and down a set of stairs.