If you are a legitimate 3.0 guy, you have two choices: 6.0 mixed or 7.0 mixed.
I would suggest 7.0 mixed. You will get to face 3.5 and 4.0 guys, and that will be fun. You will have a 4.0 female partner. She will not knock the fuzz off the ball, but she will be much more consistent than you are. You might do very well.
One suggestion, though. Please don't assume you should serve first just because you are the dude. If your serve is wonky, you two might do better having her serve first, especially if you are good/imposing at net.
I have played with 3.5 guys, and they always assume they should serve first. They are correct in all situations so far except one. That guy couldn't get his serve in to save his life. We did much better holding when I served than when he did so I obviously should have served first.
Needless to say, that didn't happen. Needless to say, we lost.
-- Random Error Generator, Version 4.0
-- Master Moonballer