Beagle

If your cruiseship has a Starbucks kiosk, that may open up more options for specialized coffee/brews. The standalone Sbux does NOT take the RCI coffee card, but does take the Starbucks card for payment.

If you have booked your main dining or special dining ahead of time, the ingredient list can be checked ahead of time to clear / verify for documented allergens. And in the Windjammer, with advance notice, the staff can plate your son's food from the back of the kitchen (to avoid accidental cross contamination with tongs by guests). Same with the frozen desserts, the ingredient lists can be checked by staff if some communication is done ahead of time. I found RCI very careful with their menu ingredients.

Went to Cozumel's Paradise Beach last December, and the service was low-key but attentive. Menu prices were reasonable for casual but very competently made food.. You'll see lots of towels hanging on beach chairs from the different cruise lines represented, and lots of loungers in the shade, or sun. Water was fine with just swimsuits and water shoes. The pricing for beach toys at $18/day also moderate (for cruise comparisons) https://www.paradise-beach-cozumel.com/team-post/beach/

There is generic shower soap that will get you clean, but not conditioned for the balcony rooms that we've stayed in. @johnjr Bring some of your own favorite wash, as the generic gel is only 'meh' for getting a good lather going.