OKC does not have an option for "couples" seeking.
Best bet I would recommend is you each post your own profile, and include a note showing the partner's profile as well, and that you would be looking as a couple.
I have seen mods delete profiles that were from couples. And it would be hard to find matches as I'm sure you both would answer the questions slightly differently.
Just be honest about yourself and what you are seeking in the profile.