I'm specifically looking for another prefix that has the same or a similar meaning to "exo".
Given that exo- has the following definition:
External; from outside.
I would go with either extra-:
- Outside; beyond.
1.1 Beyond the scope of.
- attributive Outside; external.
‘the outer layer of the skin’
‘the outer door’
I will note that outer is an adjective rather than a prefix.