200mW is indeed a bit weak if you want to do more than a couple hundred meters. the TS353 400mW or ImmersionRC 600mW are both plenty of power (with proper antennas) to go 2km or more in a low-interference environment.
Right now how is your kit all tied together? did that kit come with some sort of plug and play cable for the transmitter? can you send a link to the kit?
OK so say you pick up a TS353 or IRC600, you may or may not need a $10 PnP cable based on the above question... not sure if we can use your existing cable or not but it's only $10
after that comes antennas... antennas make or break a FPV system they're really the most important part imo, so premium is the way to go. FPVLR makes some amazing kits to put a top quality omnidirectional antenna on your transmitter, and then 2 additional antenna for receiver: a pinwheel (omnidirectional, shorter range) and a helix (long range, directional).
So for example if you got a TS353 and the FPVLR antenna kit (including the PnP cable that's about $160 or so) that's easily a 2.5km+ FPV system again, in low interference environment. In a high interference environment (over a major city for example) with that same kit you'll lose your actual Remote Control before you lose FPV.