I had pretty good experiences using WP-CLI and the WP-CLI plugin MU-Migration. You most certainly have to install the latter, depending on your environment the former too, consult the documentation on that.
Afterwards exporting can look like:
wp mu-migration export all site.zip --plugins --themes --uploads
wp mu-migration import all site.zip
This is the most basic rundown, more parameters are available. The documentation, linked above, is informative and straightforward. Just to clarify, this works for migrating a single site to a multisite setup too, see the following article for this scenario and a general rundown, the article will be helpful to get started.
Obviously backups are mandatory for any crucial operation, so better be safe than sorry.
In my opinion those are great tools, which can make your life much easier, maybe you want to take a look at them.