Stupid q? Smartphone wifi only, no sim?

What I'd like to do is get a dumbphone with my same number for everyday use... but I want to keep a very pared down smartphone for work (I need whatsapp which I'll have on my work laptop) and a couple of apps like banking, for me to use a couple of times a week. I was resisting because previously I was paying for two sim cards with data etc. which I don't want to do. But can I just move my sim into a dumbphone and use the pared down iPhone without a sim on wifi at home? That would work super well for me I think...