You might want to do a search on "natural burial". This IS allowed in some areas, with the intention that the body is allowed to decompose, and any coffin is also biodegradable, with no vault used. Such cemeteries are likely to be more wild, rather than manicured lawns, so subsidence isn't a real problem.
I was exploring the cemetery next to my hotel in Pennsylvania awhile back, with graves going back to at least the early 1800's. Yes, the ground was "less even" in the older sections, though I think some of the areas had had some additional fill put in over the years. What was particularly noticeable was that there was a certain "odor" in a few places, that turned out to be burrows where some animals, probably woodchucks, had dug down to the burial. Along with the freshly dug earth was bits of old cloth, and in one case, bone.
So, if you are going to be buried, if there isn't a grave liner or vault, you might want to seriously consider a corrosion resistant steel coffin rather than one made of wood, unless you don't mind the idea of bunking with our furry friends eventually.
My parents were both WWII veterans, so when Dad died he qualified for a spot in the local National cemetery. A veteran in her own right, a niche has been reserved for Mom next to Dad. If she hadn't been a vet, she could be put in the same niche in the columbarium with him. We chose the columbarium rather than a burial out on one of the lawns because it was a much prettier and calmer area, with a nice view over the lake, rather than being in the middle of a whole bunch of uniform and too tightly spaced headstones.
In the attached photo, the niche panels shown haven't been engraved yet, hence the tags. A month later, almost that entire wall was filled, mostly with WWII and Korean War vets.