@JDW goes over options in his video
There's the Fanny Mac - which sits on the top of your mac. There's one on ebay for $25 shipped now. If you have or know of someone with a 3d printer you could make your own
https://tinkerdifferent.com/threads/fanny-mac-clone-community-feedback.1826/ via
@Stephen
IMO If you're not leaving your Plus on for hours and hours - it's probably OK to run it without a fan. I do have a Fanny Mac just because I picked one up with a box of things, it does have power buttons in the front so thats nice, but the fan is quite loud.