If you use 47 GB on your old phone today, then 64 GB is likely not enough for the next few years. iOS can automatically unload apps that you haven't been using and compress photos that you haven't looked up, which slows things down a bit when these apps are used or you look at the photos, but saves space otherwise, but I'd think I'd go for 128GB. Note that you have the choice to either spend £50 more on an iPhone 11 with 128 GB, or £50 less on an iPhone XR with 128 GB.
Compressed photos means: If you look at one of your 10,000 photos that you haven't looked at in years, it first looks a bit rubbish and within a second or two looks good, because the high quality version is being downloaded automatically when you look at it. Unloaded apps mean: The app looks as if it was on your phone, all the data is there, but when you tap on it it must be downloaded from the internet first. That's Ok if you tend to download apps and then never use them, and the ones that you use won't get unloaded.