If your AK comes with an EG1000 motor, then it will handle an M110 spring fine with a 9.6v battery. (should be able to pull it on an 8.4v as well)
At the least:
metal bushings
M110
reshim/regrease
Middle ground:
Metal bushings
M110 spring
Metal bearing spring guide (TMs come with a plastic spring guide, so it's a good idea to swap it out for a metal bearing spring guide)
Also a good idea to adjust the angle of engagement. (google it if you don't know, there are plenty of guides)
TM gears aren't designed for stronger springs, but I have "heard" (keyword) that they can handle M110s reliably. If you want to be safe, install a set of JG, XYT, GE, SHS, or some other durable chinese gearset along with the other upgrades mentioned above and you'll be fine.
Ehobbyasia.com is a great place to buy upgrades. They have excellent prices.
Me personally, this would be my list:
Deans connectors
Guarder SP100 (basically an M110 spring)
SHS, super shooter, etc metal bearing spring guide
G&P 6mm metal bushings
G&P shims
JG, XYT, GE, SHS, or some other ACM gearset
Element POM piston head.
If you really want to save money, you could get an Element FTK and an M110 spring. Element FTKs have some nice parts (piston, piston head, gears), but the bushings and spring guide are not the greatest. (spring guide has a weak plastic shaft)