Stock cooler on k series CPUs won't be able to help your CPU with good temps. When you will overclock it, you would need better cpu cooler than the stock cooler.
Depending upon your budget, number of RAMs, case, motherboard, you can opt for air cooler or water cooling kits. Some recommendations are: -
Noctua NH-D14/15, NH-U14S/12S
CM V8 GTS/Hyper Evo 212
Corsair H100i/H110
Swiftech H320/220
Let me know your number of RAMs along with their model/serial number, motherboard model, and Case make/model along with preferred cooler so that the compatibility can be checked.
Most of these coolers come with thermal paste, so you don't need to buy any.