Hi Sleepyjoe,
While this happened to you sooner than it would for most people (and in some cases this can be because you made a comfort choice that was already “on the edge” of being too soft for you … see post #2 here) … most of the major brand mattresses use lower quality materials in the comfort layers and early foam softening and the loss of comfort and support along with “virtual” impressions that aren’t covered by a warranty aren’t uncommon at all after a few years (sometimes sooner as in your case) and is one of the reasons I would suggest avoiding them completely (see the guidelines here).
The first place I would start your research is the mattress shopping tutorial here which has all the basic information, steps, and guidelines you will need to make the best possible choices … and know how and why to avoid the worst ones.
The better options or possibilities I’m aware of in the Bellingham area are listed in post #14 here. There are a wider range of options in reasonable driving distance in the Seattle region in post #2 here or if you are comfortable with cross border shopping in the Vancouver list in post #2 here.
Phoenix