Air tight smart speaker options

I’m switching my stuff from Google Home over to HA namely for privacy. I want to have the entire smart home setup on an isolated LAN. As such, I want to find a new setup for the smart speakers since Google Home has to be connected to the internet. I’m a big fan of having the voice control throughout the house. Any recommendations on how to build something like this or something that natively can do this?

I have assist setup, but I’m not sure how best to implement it hardware wise throughout the house.

HA does not currently have the complete voice assistant up and running.
I would probably wait to end of the year to get hardware, so I could utilize the last few features too.

If end of the year is too far away, then at least wait for chapter 4 of the year of the voice, which should be here on oktober 13.