You should just buy an automatic vehicle. if you've got the skills and resources to swap transmissions then you can also change vehicles.
The main issue is the wiring. You'll get hung up there. It's not all mechanical, plug and play easy. It'll be a lot of wire parsing and merging.
Parts required:
Transmission, rear driveshaft, shifter assembly/linkages, complete transmission and engine wiring harness and TCU, transmission cooler (either snag the radiator or add an aftermarket radiator) and pedal cluster - they just unbolt as an assembly but aren't the funnest thing in the world to remove.
Parts that make it nicer, but aren't necessary:
Interior trim/console to trim up the shifter, instrument cluster so it's got PRND and appropriate stuff (but it's not necessary), and the cruise control computer if you want that to work
ECU's are not transmission specific so they don't need swapped. they'll need the appropriate identifier pin modified or just install the body side wiring harness for an auto then you'll have the correct pin/wiring and ease your merging pains.