I would suggest Asia for the affordability, and in here Thailand (not the cheapest but most developed services around the neighboring countries).
It seems Cambodia and Vietnam are quickly developing and are way cheaper than Thailand so it's mostly about your own preference.
It's all year warm climate, beautiful nature and cheap living in all of these countries. If you get any pension you find it easy to live anywhere here.
The best medical and professional services are in Thailand as here is already a huge population of people from Europe, USA and Australia consuming those services, but neighboring countries are not coming far behind.