Lightweight tablet suggestions

I would suggest going to the gym.😉

I agree, but who wants to go to the gym when I can sit in my recliner and listen to music. 😉

Buy a used older IPAD Mini.  . I rep a few lines off the off brand Android tablets you speak of.  They all tend to be a little slow, have not the best radio in them,  Doesnt matter , Supersonic, RCA, Packard Bell, Lindsay, Ematic, Core Innovations and I can go on .  Primarily all the same tablet spend a little more and get an IPAD nothing like them.    If you wantedto go the lower end route I can sell you one brand new in a box for $40 plus shipping. Up to you Plastic Housing like you said android based. as just a remote maybe ok

Good suggestion on the iPad Mini.  I've always been put off by Steve Jobs/Apple but as a remote control, it will give me a chance to see what I've been missing.  Who knows, maybe I'll be a convert!  I'll check it out.  I'll never forget an early iPhone model that lost reception when it was held a certain way.  Steve Jobs response was a snarky "don't hold it that way".

i use an 8" kindle fire for my kitchen system--you can pick one up for 70 bucks or so. good interface; wifi or bluetooth streaming works fine

This should help: https://www.gsmarena.com/search.php3?mode=tablet

You can sort them by weight / size, etc. 
any important spec that you want.