It's not about adding up what you have and calling it a team. You could designate a physical wall and a special wall to your team, but if they happen to be Skarmory and Blissey, then Infernape destroys your entire defensive core like it were a dry sandcastle. I run strictly offensive team with one tank, and all I have to do to get around the opponent is use what resistances I bought myself in choosing strong sweepers. By all means, go ahead and run a couple walls to be safe, but all I'm saying is that there is no algorithm to how this game works. In fact, a lot of matches are won by a slight stroke of luck in the form of paralysis, a critical hit, a lucky burn, winning a Speed tie, etc., and you can never account for it.
Well, anyway, just wanted you to know that. If you do want a special wall, you might as well go with Blissey, and if you want to keep sweepers alongside her, you might be interested in making her a cleric as opposed to the new standards. Also, you'll need to protect her from physical attacks and her Fighting weakness really well. Even though he doesn't resist Fighting, Hippowdon is usually a great physical wall to complement Blissey, as the Grass, Ice and Water type moves that hit him super effectively are typical special, and thus awards you an easy Blissey switch-in. Of course, Hippowdon is still going to get beat up by Infernape pretty badly, so perhaps you may like having something that halts him from lobbing his fecal matter at your walls' faces.