I would recommend getting the original SE for the size and it will run iOS 13.
Since the OP already has the 6 and is happy with that size, OP should get the iPhone 8, massive upgrade coming from a 6, or better wait for the SE2 which is coming next year supposedly, and it has even more stuff.
The current iPhone 8 doesn't have the latest tech, but it's way better than the SE or 6s. You do not need every single little thing that is new of course, but still, the Camera and Camera Features, Performance, Display, Speakers etc... that's a massive jump, but you need to want all that stuff. I wouldn't get a SE anymore, unless you really really want that 4" form factor. It's a smaller 6s, and 6s is quite old now. Who knows if the SE / 6s is going to get iOS 14? iPhone 8 is just a massive improvement in every way and it's only 449$, and it should be improved by March 2020 with a new chip, more RAM etc... for 399$. Don't know if the rumor is 100% true, but that phone could be worth it, and it looks like the OP wants exactly that SE 2 when it's coming, so yeah, i would wait aswell and not get a new iPhone right away.