Go read https://www.mrmoneymustache.com/blog/ if you filter out the snarky “I’m so badass” posts there’s actually good advice in a ton of topics such as health insurance / coverage, investments, and how not to be a wasteful person mostly :)
Buy it on the ACA exchanges? Depending on your income, you may qualify for significant subsidies. Taxable retirement income for a given lifestyle is lower than most people seem to think -- dividends and LTCG have a lower tax rate than income; you don't pay taxes on the cost basis; you don't pay taxes on withdrawals from Roth accounts at all; and you don't need surplus income to save for retirement. If you live in a paid-off house, that can cut Cost of Living (CoL) needs substantially (e.g., the mortgage is something like 75% of my pre-retirement spending in a High CoL city).
Like what is stated elsewhere, when my wife wasn't working, we were on the ACA exchange. She's now working for fun again at a company that offers it as a benefit and so I'm on hers as it's a slightly better plan at a similar price to an unsubsidized ACA plan.
