I access lemmy through Firefox, and I just have bookmarks for all of my accounts and have whichever ones I’m using the most pinned. Switching from one to another is just a matter of clicking a link.

I don’t know of any way to combine everything into one feed, though I wouldn’t be surprised if one or more of the apps will do it. That’s exactly the opposite of what I value though - I don’t want just one feed - I want whichever feed I happen to be in the mood for at the moment.