This is the best! Searched for years…low profile pillow
https://www.amazon.ca/gp/product/B07YWF6J4H/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1 I just received this one and it's very flat and firm and has a cooling side. I actually got it to put under another softer pillow to build up the height but it sounds like what you are looking for. It's very flat and firm