Same situation when I applied last September. Here is what I did.
I paid $30 VOS (verification of status) fee (online) and attached the receipt with a brief expiation on my citizenship application. Mailed both application same day. I got my VOS as email attached on Feb, few weeks before my oath. Remember you may not need VOS for your test or interview (I didn't have it during interview) but you need it during oath. Hope this helps.