How comfortable are you with the Right Start methods yourself? I'm unclear if you have taught it before or if this is your first time through. If you really want a formal math curiculum, then I think Math Mammoth 1 could be a suitable spine. Mari. a uses a similar approach to math, though with less explicit instruction about when and how to use the manipulatives, so you'd have to know when to add them in. Either way, it is an inexpensive, thorough math program. Just be warned it contains WAY too many problems for some students. You have to be comfortable assigning only some of the problems or you risk wearing your child out with repetition! (I learned this the hard way!)
Or, if I may be so bold, consider teaching yourself the RS methods, and then casually teaching them to your child while you play as many of the games from the RS manual as possible. Hindsight being what it is, this is the approach I would have taken with myself... As many math games and "mom instruction" as possible throughout kindy and the first part of 1st, moving to RS B/C for the end of 1st and 2nd, and then starting Beast Academy in 3rd. Most kids don't need 3 solid years of addition and subtraction, and Beast does such a good job with multiplication and division (all topic, really!), that I would take a more relaxed approach in K-2... Just some thoughts from someone who has also started with RS.