There aren't really any bolt-on turbo upgrades that will yield you anything useful. The CT20a is actually on the big size for this motor believe it or not.
A nice upgrade would be a TD04L-13T from a Subaru. I have one that I'm planning to install at some point. It has a much more efficient turbine, so will spool faster than the CT20a. Compressor has more fins and is slightly larger, so will easily flow as much as the little motor could possibly need.
If I were you, I'd just buy one of the cheap Ebay CT20a units for now. I've been running mine up to 20psi for years with no issues. Invest in other things first like an intercooler instead.
There is no easy install kit you can buy, so it'll have to be a custom install. No matter what you do, make sure you go with a front mount intercooler. There was a lot of discussion in this thread about different options (with pictures). I went with a air/water style, but a well designed air/air would be cheaper and just as effective. Opinions on this water to air intercooler for LJ78 / 2LTE?
Yes, that's right. And keep in mind 2" intercooler pipe is plenty; most people go overboard on pipe size which makes everything way too tight. If you don't have someone that can tig weld it for you, you could probably make it all work with silicon couplers and clamps.
Just look for a 2" aluminum pipe ebay general purpose kit that comes with couplers and clamps. You can buy an ebay intercooler too, or just watch your local classifieds for one that will work. Many are too wide for the LJ, so take some measurements before you layout hard earned cash. I think mine was 26"x7"x2".
Install a pyrometer too. Once you've done an intercooler and pyrometer you can start tuning for a lot more power and still run lower EGT's than factory. Depending on how stock your exhaust is, that would be a good upgrade at some point too (2.5" is perfect).