Two tips:
- You can use many apps at once with the same account. Just install additional apps and sign in on them too. (Bear in mind though if you have notifications switched on for all of them, they will all notify for the same thing.)
- You can use many accounts at once with the same app. The official Mastodon app and some third party apps let you add or switch accounts by holding down the icon in the bottom right corner. Some apps will have a different interface.