Indonesia is becoming increasingly popular with expats, but healthcare standards are unlikely to be nearly as high as people from the United Kingdom might have become used to. As such, you really need to know what to expect before you move out there.
Indonesia does have a national health insurance scheme. It was started in 2014, and universal coverage is theoretically provided for all Indonesian citizens; in fact, this is set to become the largest health insurance scheme in the world by 2019. However, expats are not covered under this scheme, so if you are going to live there you will need to arrange private health insurance. If you hold a temporary resident card (KITAS) or retirement visa, you will be legally required to have private medical insurance.
As a developing nation, and a rather large one, healthcare facilities in Indonesia are often substandard by British standards. You will find some good hospitals in Jakarta, but healthcare facilities away from the capital will usually be quite poor, and even public hospitals within Jakarta will often be overcrowded, with long waiting times considered a fact of life. This is another reason why you need to go private. Luckily enough, there are plenty of established expat health insurance providers that understand the Indonesian healthcare system and can deliver outstanding coverage.
You may also investigate healthcare insurance providers that can cover nearby countries. Many expats prefer to visit neighbouring nations, especially Thailand and Singapore, where they will find better medical facilities, though this tends to only be for planned or routine procedures.
You should be able to find a wide selection of over-the-counter and prescription medications in Indonesian pharmacies. Pharmacies are usually found in shopping malls and throughout larger cities. However, one thing to keep in mind is that pharmacies at hospitals and clinics will require prescriptions to be filled out by a doctor from that exact practice. Additionally, keep in mind that most Indonesian pharmacy workers will speak very little English, so you might experience trouble trying to communicate.