I've researched this and I'll be buying a Kobo once my Kindle finally dies (it's lived a hard life). I've bought DRMed books from some non-Amazon sources and had to go through the steps to strip their DRM so I could read them on the Kindle - this was using Calibre. Mostly those other sources were using Adobe Digital Editions (DeDRM can handle it).

I have yet to find if there's a self-hosted option that would replicate what Amazon does - i.e. tracks read position and lets you download and read via an Android app or a website. I do have Calibre-web set up, but haven't fully looked into what it can do yet.