Thanks for all the great replies!
Why not use one of the headerless Arduinos? Like a Promini? Not much more than a microcontroller there.
A Arduino Pro Mini is super small.
I bought a pro mini clone on Ebay for less than 5 euros.
But you need a seperate usb-to-ttl-serial converter to upload the sketch.
A Arduino Nano has a usb connector, so you don't need extra hardware.
There are more options. Like the Arduino micro, very small, and it connects to the usb.
I've looked into this but there always seems to be a slight difference that scares me from my Uno. Any suggestion on what a good but small solution would be for a beginner?
My projects are usually embedded, no PC connection when running, so I regularly have USB/Serial off board for programming.
If end user is not intended to reprogram them, I'll go even farther and only put on an ICSP header and then skip the bootloader.
The end user is not intended to reprogram my project. What exactly is embeded?
I had considered this route and is what I originally planned on. Do you need a socket to solder a IC into perf board or can you solder the small legs on them?