I don't think anyone can really answer your question for you.. Which phone you upgrade to is completely your preference and what you can afford.
How much you pay per month is not something we can determine.. and we have no idea what you pay now.
If you want to save money on your 'unlimited package'.. that sounds like something you should be talking to your carrier about.
Here is a link that will allow you to compare the iPhone models you mentioned. You can select various models in the drop down to compare side by side
https://www.apple.com/iphone/compare/?modelList=iphone12pro,iphone13pro,iphone13mini
The 13 pro is not all that much different than the 12 pro. so if that's more budget friendly for you, go for that.
The mini is a bit smaller. Do you think your 11 Pro is too large?
The 12/13 pro models are the same size as your 11 pro (0.1" taller, no wider) and gives you 0.3" more screen size.
If you have a store nearby with display models, you could go and see if the mini size is right for you.
Do you need the pro model? One of the main things you get with the pro model is a better camera. But if you are considering the mini, you must not need the pro model's camera? So have you considered a 12 or a 13 non-pro model? it will be cheaper..