Firstly I say, leave your settings as is.
As mentioned , you are using iMessage ......blue bubbles.
Texting should still work “if” you send to a phone number and not an email address and “if” you receive on your phone number. So in your message settings......send/receive, only check your phone number...leave the registered email addresses unchecked.
Make sure your phone has most recent iOS update.
iphone should switch automatically but not always.
If you have limited data, then of course leave it off and do the occasional check for iMessages and turn data on, then of.
Both wife and I have iPhones, an 8+ and an XR and both of us had data off and no wifi connection and green bubble texting worked with no changes to settings.
