Health insurance is the most important practical purchase you will make before a long stay abroad. A short tourist visit to a doctor in Japan or a brief hospital stay in Thailand can cost thousands of dollars without coverage — and serious illness or an accident without insurance can be catastrophically expensive in any country.
The right insurance for a slow traveler is different from a tourist's policy. You need something that covers extended stays, doesn't exclude "pre-existing conditions" defined too broadly, and ideally covers repatriation to your home country if needed. Read the fine print on any policy before purchasing — specifically check whether it covers the activities you plan to do and the countries you plan to visit.
For stays longer than 6 months in a single country, look into local health insurance options. In Portugal, private health insurance is available from around €80/month and is often required for residency applications. In Colombia, enrolling in the local system (SISS) is often mandatory for residents and can cost as little as $50/month. Local coverage is often better value and more practically useful than international plans for long-term stays.