Hello! I found this forum to be so helpful in 2015 when I bought my mattress. But alas it is now time to get another one, as the mattress has developed a dip in the middle (on one side) that is getting unbearable and contributing to chronic neck and shoulder pain. Thus will not be flipping it anymore. That’s what I get for going with a pillow top, even though it was a fairly firm-ish pillow top at the time, on a double sided innerspring mattress. Going mattress shopping Saturday, back to the same company that does double-sided mattresses and def won’t get a pillow top this time!
Hi Vicky.
Welcome back to our Mattress Forum. 
Sorry to hear your mattress has started to sag and is causing pain. That’s not fun! Do you have any questions going into your mattress shopping experience that we can help you with?
NikkiTMU
thanks NikkiTMU! I guess when I go look at mattresses I will get specific specs (such as foam density etc) and check back with the forum to see if they are good. So my plan is to find a good quality innerspring mattress (not too soft but not the firmest either), and add a foam topper to relieve pressure points.