First, I'm sorry about your niece, but glad she led you to a place of happiness and I assume a place she enjoyed. Not sure if this is the town you mention north of Tulum, Akumal is a little farther, maybe 30 minutes. It's a nice beach town and we thoroughly enjoyed our vacation nearby a couple years back. We stayed at a beach house with friends a good solid beach walk south...maybe a mile or so.
According to our friends Akumal has developed quite a bit over the last 10 years so not sure if your cup of tea. We liked it though. There is a 2nd level open air restaurant just after you enter town on the left called Taverna Akumal that we enjoyed. We ate seafood in one night and took pizza out another. Owner Alberto Lombardi was there both nights, very engaging guy, has multiple restaurants around the U.S. There is also an ice cream/bakery shop and multiple other restaurants on an off the beach.
We had snorkeled out from out house during the week with no turtles, but once we went up to Akumal Bay the last day we saw multiple turtles, made my daughter's vacation. The nearby cenotes were cool too, we visited several of them. Definitely a different lifestyle!
I always try to read a book set in the areas we visit. A novel I read while down there is Xtabentum - A Novel of Yucatan gave some history and flavor of the region.
You weren't just on HGTV were you?
They just had a beach house episode based in Akumal, someone told me about it but I missed it.
Hope you find your dream spot, there are certainly worse ways to spend time. You should still be able to squeeze in some boating time on the water down there too!
Good luck in your search.