[Edit] Currently looking at Element.io. Any thoughts on that? Based on matrix.org.
An easy way to deploy a matrix server is through Freedombox [1]. After installing it, enable Matrix and Coturn [2] in the dashboard and enjoy.
By the way, if you don't want to use FCM then download Element from Fdroid, otherwise you can download it from Play Store
Warning: Be careful using the API to delete all history of a room, there may be bugs.[3]
[1] https://wiki.debian.org/FreedomBox/Hardware/Debian
[2] https://wiki.debian.org/FreedomBox/Manual
[3] https://matrix-org.github.io/synapse/latest/admin_api/purge_...