We booked the base room on spg (Oceanfront Cabana), which aually is not their lowest room type ... some cabanas don't have ocean view or even own bathroom at all. Wanted to try it and had quite low expectations but the cabana was much nicer then expected.

Room picture:
Pretty small, but cute, great ocean view (sunrise from the bed), 20meters into the sea, and a very good moscito net. Bed was okay, a bit small for 2 adults. Food was VERY good; staff friendly but very casual. I would avoid weekends and foolmoon as there are big partys.

We also stayed at the Design Hotel in playa del Carmen and can recommend this cute boutique hotel as well (but as you wrote, it's adults only).