Homeschool-feeling accomplished

After an extended thanksgiving/christmas break,we finished a reading textbook we have been reading for the past 6 months.I feel soo accomplished and proud of my son.I'm not really sure what grade level it's on but I showed it to my sister who is getting her teaching degree and she said it looked like grade 2-3 level.Zachary is 7 so that's fabulous! I'm looking for something comparable to that and am having problems finding anything.The book we just finished is an actual public school reading textbook-RAINBOW SHOWER by Scott/Foresman/and company and says level 5 on the back of the book but I do not know if that is the actual grade level or exactly what that means.The stories have been perfect for Zach and he has really enjoyed reading them.I do have some workbooks and other books we can read until I find something that will suit us but it is frustrating.There is the library too but sometimes getting out to it is a pain.He is also doing quite well in math.He is doing addition (double and triple digit problems) in his head.We will ask him a question and he'll answer so quickly.The other day we were at the pharmacy and spent like $55.The pharmacist asked him how much more would it be to make it $100.He answered 45! They get a kick out of him-they are always saying how smart he is.He is also doing multiplication in his head.So I'm thinking about bumping him up in math but want to make sure we don't skip anything along the way.We've been taking it slowly this week trying to wean him back into the study routine.