I bridge SMS to matrix, I currently have no use for slack, but if I were forced to use it I would bridge that to matrix as well.

Of course the matrix IRC bridges are also quite good. I'm in a couple of bridged IRC rooms.

What do you use to bridge sms to matrix? I've seen a couple projects people were working on, but some were very hacky, and the rest were lacking features.

I use the one by tijder: https://github.com/tijder/SmsMatrix

It works well enough for me, though I don't use SMS too often though.

What I did like is that I can add another account to a room such that I can monitor texts from both matrix accounts.

And I'd replace Slack with this thing. To each their own :).

Can you impersonate Slack users the same way you can with IRC, to give each incoming SMS’s author its own user account?