I haven't used the Rotosounds either but I've had almost every set of Innovation strings available. (Silver slaps, Super Silvers, Honeys, Rockabillys & Ultra Blacks)
I'd suggest trying Super Silvers first - decent enough pizz tone from the E and A but still flexible enough to slap.
Another option (and my current go-to string) would be Thomastik Spirocore Weich. Very defined, warm pizz tone but surprisingly slappable for an all-steel string. Plus, if you don't like them, you'll have no trouble selling them.