Not sure if this is what you are looking for but I am a back sleeper and sometimes side. This pillow is gusseted which provides great support without forcing your head forward. The fill is shredded memory foam and can be added or reduced over time or replaced entirely. To me the secret is the gusseted shell. Amazon - COOP pillow
I actually grew to love the sleep number, after seeing a few doctors I uncovered what was causing my back pain which is an inflammatory disease called ankylosing spondylitis. Super unfortunate diagnosis but after getting on the right medication for it my back pain has all but disappeared and I started to really enjoy the sleep number bed.
I'd suggest just trying to mess around with the number settings as best as you can and get a pillow that works for you. I ended up going with a cervical pillow from Cushion Lab that works pretty well for me. I also got some Coop Home Goods pillows that allow you to adjust the amount of memory foam in each pillow. That also helped me find the right mix that makes it a pretty comfortable sleep.
Wish I could be more help, beds are a weird mix of preferences that some people like and others hate. I remember buying a cheaper pillow top mattress that I thought I would enjoy but I ended up returning it and going back to the sleep number.
I must’ve tried 20 different pillows before finding this one. I’ve had it over a year and I still love it!
I usually have about a dozen folks on site. I went and bought a bunch of pillows and moved em between folks and had people tell me which ones they liked the best. To be clear, if a guest asked me for a down pillow, I would just run to the store no questions asked as thats my policy for low level cost shit. I got the new pillows precisely because people were complaining about the ikea/target pillows whether it was filled with down or something else. I literally burned through and tested 15-20 pillows over 2 years with guest feedback.
The problem with down pillows is they often lay flat. Its not supportive, and then you get into the occasional person who is allergic. The problem with cotton/microfiber stuffed pillows is they get clumpy, they aren't even, and they are generally worse for heat than the below ones.
Now the first one is more my guilty pleasure. It's better than the second link, but the second link is the one I used for my guests (and I made a mistake, those are only $20 each though I seem to recall paying 32 last time.
https://www.amazon.com/gp/product/B01LZHMODV/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 is what I use for myself. I even have a travel one I bring with me when i'm on flights or going to spend a lot of time in the car. (all the time!) This fucker even comes camping with me lol.
https://www.amazon.com/gp/product/B07KMW8ZSN/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 is what we have for guests.
These can be adjusted to be as firm or not firm as you want and we keep a small bag zipped up with extra material just in case.
In all fairness, I just got my costco membership about 3 months ago. Id be curious to check out whatever pillows you are getting from there. We are probably going to be getting our sheets from them instead of of the thresholds we get right now if they are comparable. We're just waiting for us to need to buy our next new replacement set to try em out.