You don't need to self-host a Matrix server.
Just to be sure:
- Matrix server != Discord server
- Matrix Space/Community ~ Discord server
Matrix Spaces/Communities are handled inside a Matrix server.
You can pick just an existing one like the matrix.org one ( bundled by default when you access to https://app.element.io/ ) and create an Space/Community there which is equivalent to Discord servers.
Edited: hosted bridges for Matrix<->Discord already exist, https://t2bot.io could help with it.
I have already bridged successfully different rooms from Discord and Telegram.