As with some others, Bonaire leapt to mind as the obvious go-to, but Curacao is a strong option.
My Research Notes for Bonaire -
My Research Note For Bonaire
8 Day Trip Report: Sand Dollar, Dive Friends (a popular option, and one I enjoyed).
2022
Trip Report Bonaire Trip Report - V.I.P. Divers/Aqua Viva Suites (this was a deliberately budget-minded trip, and what I'd like to do again).
Curacao Trip Research Notes
Curacao Trip Report with SB Surge Jan. 2019 (pricy but fun).
If I were going alone and diving was the sole focus, I'd consider All West Apartments or Nos Krusero and use Go West Diving as my supplier, on the condition that they are still okay with solo diving (in the past I got the impression they weren't thrilled, but would allow it). If I based in the Willemstad area, I think Dive Bus is okay with solo diving. I don't know to what extent solo certification matters.
Someone mentioned trying to rent a pony on Bonaire without a solo cert. might be a hassle. I take my own 3-cf Spare Air, which is small, light, easily transported and I can fill off a rental tank myself without asking a dive op. staffer to do it. I believe they now have a 6-cf option.
Spare Airs get a lot of flack on SB, and they have their limits. Shore diving Bonaire, I'm not worried about returning to my point of entry, just some breathing gas to let me head up top at a more deliberate pace should the need arise.