I used to have alias rm='rm -i' for a few years to be careful, but I took it out once I realised that I had just begun adding -f all the time

Yeah, but that's because it's implemented poorly. It literally asks you to confirm deletion of each file individually, even for thousands of files.

What it should do is generate a user-friendly overview of what's to be deleted, by grouping files together by some criteria, e.g. by directory, so you'd only need to confirm a few times regardless of how many files you want to delete.

See also rm -I (capital i), which only prompts when deleting directories or >3 files