My solution is to run with as few as 2+me (the DM), and use a play structure that doesn’t require the same players to be present at every session. We always end rhe session in a safe location (town, safehouse, etc). If someone can’t make it, they’re just in suspended animation along with their gear and hirelings/retainers until they’re back.

Just not sweating the fact that it’s a game has gotten me a very consistent game every two weeks like clockwork.

What’d you end up picking? I was going to suggest just trying to get used to OBR 2. I agree it’s not as wonderfully minimal as the original, but it’s still not nearly as top heavy as Roll20, Foubdary and the rest, and the accounts, at least, are free. I’ve been running a megadungeon in it and the learning curve is pretty shallow compared to everything else.