One reason I went with a Samsung Note (the 3, back in 2013) was because I have fat fingers too. The stylus made typing a lot easier. These days, I wouldn't buy the Note 8 (my personal preference - I prefer a phone I can replace the battery in, but I'm afraid that by the next time I upgrade, there won't be any). But there are styluses you can buy for a few bucks for a few of them (3 to 5 in a pack) that will work on any phone. They have clips, so you can keep one in a shirt pocket. (Try eBay - unless you need one now - then try Amazon, but you'll pay more.)
The OS doesn't really matter - the on screen keyboard is still going to be about the same size for the same size screen. And they don't seem to be making phones with physical keyboards any more.