My experience with Matrix is that the federation itself is a deal breaker. I have a pretty beefy server and good connection which was getting ddosed by running Matrix and timing out on so many requests for avatars/profiles etc. Maybe I did something wrong, but the whole experience rendered me quite skeptical to the viability of it as a federated chat.

That said I’ve had nothing but good experiences using it with big servers set up by pros.

I’ve been happy with Fastmail for 10 years, though they’re Australian and not European. Might look into a European alternative at some point but so far I’ve had no reason to switch.