My top choice would be Siem Reap, Cambodia to see the Angkor site. Bangkok is a better launch point, but S'pore is ok.

Bali is another good destination. I'd avoid Kuta and Nusa Dua and go to Ubud and from there North to Lovina or East to Candidasa, but I think that may be a minority opinion here.

Sri Lanka is great. I found lower end places just fine, the food great, and the people very friendly. Kandy is a good base. Ella and Mirissa are nice. Travel is pretty easy and cheap using public aircon bus and 2nd class train. A driver + car is helpful going from, say, Kandy to Ella to Mirissa or Galle.

Another possibility is Laos. Vientiane is ok if you have time to take the bus from there North to Vang Vieng and then on to Luang Prabang. Otherwise, just go to Luang Prabang.

Myanmar/Burma is close, too.
Rich