I think this is a very basic grammar question, but I'm stuck with how I should continue the sentences. Could someone explain it?

> 1. In Japan, I've never shopped at a wholesale store, but I **did / did it / did so** a lot in the States.
> 2. I used to read books almost everyday, but now I **do / do it / do so** only once a week.

About the sentence 2, I know that I can say, " but now only once a week." But I'd like to know which is the best if I give a full sentence.