Not sure what your gearing is now, but give me a sec to explain a few things first.
Lockers or any traction adding device is mainly the carrier part of your differential. They come in auto (Detroit locker) Electric (E Lockers) Cable (OX) and Air (ARB), and yes there quite a few more manufactures out there that I didn't mention.
In a dana 30,35, and a 44 there is two different carrier offsets. This off set is for different gear ratios, 3:11-3:96 and one that fits 4:10-4:88.
So depending on what gear ratio your stock axles have and what you want to run in the end its best to buy the carrier and new gears at the same time.
Now also stock axles are set with a factory spline count a Dana 30 is 27 spline and a Dana 35 is 30 (? not sure here), and a stock Dana 44 is 30 spline, you can buy upgraded axles with 30 spline fronts and 33 rears, but they will not work with your factory carrier.
Stock axles are strong enough to take most lockers with mild driving off road. Tire size and skinny pedal usage here plays a big role here. Axle type is another long subject...as is locker types. And there are arguments pro and con for every selection along this path.