The only reason to use healthcare.gov is if you qualify for a subsidy. The income limits may have expanded a bit from where they started but as far as I know there is still no sliding income scale for subsidies. Healthcare.gov will tell you if you qualify for a subsidy.
You can purchase from the many private insurers but even they, for the most part, will follow the ACA structure outlined as Bronze, Silver, Gold, etc. There may be some high deductible ones. I went with the Bronze coverage since I was relatively healthy and figured "why pay up front for coverage I may not use".
Since going on Medicare, thankfully I don't have to do this anymore. While I am getting hit with IRMA's on Medicare, it is still cheaper for me than my ACA premiums (1,000/mth with a $5,000 deductible) were. I only went to the doctor for covered preventive and if I had to do so.