I really want to cut out inner envelopes to be a bit more eco-friendly and save money. However, I am inviting several couples who do not live together. Several of these guests are dating people I have never met, so it feels really weird to send them a separate STD and invitation. I know normally, I would address the invitation to the person I DO know, and then list their SO by name on the inner envelope, but that's not an option for me.
Even though the SO doesn't live at the same address, is it okay to put their name on the envelope so my guests know their SO is invited? (Hopefully, they would expect that anyway.) Would I list them the same way I'd address to an unmarried couple living together?
Any better ideas? TIA!
ETA: Since I know people check these things, no, I am not sending out my invitations yet!

I am addressing STDs and trying to make a spreadsheet of addresses for my friend who is doing the calligraphy for the invitations.