The next mattress I get will be a latex mattress.
I have had 3 mattresses over a half dozen years and they all have the same issue with getting lumpy. 9” or 12” thick firm mattress from name brands.
I have not tried a latex one. I was looking at this 2-1 mattress that is firm on one side and softer on the other. You tell them how you want it. https://www.zenhaven.com/mattress
Supposedly they never get lumpy.
We just spent a $1000 for one of those adjustable beds.
I hate it.
We cannot get a good night’s sleep on it because it is soft in the middle and when you raise the head it feels like you are slipping downhill..................