I use one of the folding wooden TV trays from Wal-Mart, but I still have to sit up to sew. I would not be able to use a lap tray because I am OCD about seeing my stitching path and that would be too far down. But that's just me. You may love it. There are other foldable tables that allow a rolling, armless, office chair easy access for seeing the details of your sewing if you wanted to go that route.
https://www.amazon.com/HUANUO-HNTT-B...Q%3D%3D&sr=8-6
https://www.amazon.com/Fancasa-Porta...ae8f9840&psc=1
This could possibly be a good fit for you.
https://www.amazon.com/AmazonBasics-...4-be83d68222e9
Well dang....I found so many interesting possibilities on the Amazon site that I decided just to post the whole page.
https://www.amazon.com/adjustable-sm...le+small+table