End of contract for iPhone 8

My contract is coming to an end with my current provider for my iPhone 8. I currently pay about £41 a month for my phone and unlimited texts, calls, 30gb data and my Apple Watch plan.

I’m debating going sim only as I am not having any particular issue with my 8 (touch wood) and don’t want to pay much more for a new phone per month that what I already am. It seems the new iPhones are considerably more per month than my current £41. Can anyone suggest a reason for me to upgrade to anything above the 8?