You don't need 'the network' - meaning a cell network to download or use apps.  That can be done over WiFi.  There could be a few exceptions, but generally you just need a Internet connection.

Either a phone with no cell contract or a tablet, then use Hot Spot from your main phone might do what you want.

Maybe you're wanting a phone with a cell plan, but just don't need the voice portion of the plan?  I don't think you'd save much if you could omit voice.  Adding a tablet to your plan like someone else suggested makes the most sense.

Do you really need 5G speed?  4G is pretty fast for most things.  Requiring 5G for this phone narrows down your choices.