I really like your team. For my bench, I usually like a backup infielder, but my league has daily changes, not the H2H format. Rodriguez and Blalock will play virtually every day anyway, so I wouldn't worry about it.
As long as your league allows A-Rod to be played in the SS position (as I think Yahoo will), you don't need to get another SS. There's probably not another SS on the waiver wire that will be better than playing Blalock at 3B.