I have been reading up on doing a trip to SE Asia for April-May 2027 for my wife & I, both 69, retired and very active. We would like a similar travel experience as our previous one to Bocas del Toro, Panama, a small and basic island as far as infrastructure is concerned, a prevalence of dirt roads & simple structures, yet a wealth of nature including rainforests, lots of wildlife like monkeys and sloths, clear ocean water for snorkeling, and enough places like bars/restaurants to keep things interesting where we spent several weeks there.
We stay away from crowds, like good (but not fancy) clean accommodations, do a lot of walking in rain forests, beaches, and meeting the locals and other travelers. No interest in shopping or much in the historical aspect really.
Singapore sounds like a good jumping off spot for a couple days (~3) to decompress and take in some beautiful architecture and gardens, then to Bangkok for another couple days (same ~3), up to Chiang Mai (include Chiang Rai?/Chiang Pai? - total ~5-7 days?). Here I'm wondering about a couple days to Thailand's lesser visited islands down the (west?) coast, or skip & head to Bali? It doesn't seem like we should miss going there even though the reports of over tourism are rampant, actually in both the Thai islands and Bali, or is Lombok and/or the Nusa's a possible substitute? If we did Bali we'd likely focus on Ubud (~4days), over to Amed, maybe Lovina, possible stops including Sideman & Padangbai. If Lombok has the beautiful forests, hiking options, and beaches along with less tourism I could see staying there 8-10 days. Would we be pushing it too much to catch Flores, which seems to have nice snorkeling though the landscape looks very dry, more deserty, the Maluku islands, or possibly Sulawesi? Ultimately trying to keep this a 30-day trip, and don't want things to feel too rushed, so finding a couple "ideal" locations is the goal.
Thank you for any and all comments, suggestions, and helpful hints! Will

>> a small and basic island as far as infrastructure is concerned, a prevalence of dirt roads & simple structures, yet a wealth of nature ...

That would be not Singapore.

What mrwunrfl said ... though I'd add that Singapore holds some wonderful gardens and is, IMO, well worth a visit.

Overall, my impresion is that your are overestimating what you can do with 30 days. I know that's a chunk of time, but traveling from place to place in SE Asia can take a lot of time.

FWIW, you might find some useful information about Singapore and Bali in my old trip report for a month that started with the former and ended with the latter,
A Memorable Solo Month in Singapore, Java, and Bali

Your stated purpose and list of places do not match. You'll need to get off the beaten path. Hard to say exactly what might appeal to you. But there are an unlimited number of possibilities. Take a look at this video and let me know what you think: