Start with a polish job and a spring kit, that'll cost under twenty bucks. If you need more you can generally get a drop in trigger for a hundred-150 bucks. Sometimes they pop up for sale used if that doesn't bother you. 3.5 lb is a popular spring weight but may be too light for carry use, everyone's got different ideas on that.
I love my overwatch precision. Not sure on the weight but it takes up all the pretravel and has a really nice crisp break while still being 100% drop safe.
Best bang is a Ghost connector. I persoally avoid changing springs because I've found aftermarket springs can cause reliability issues. Feel free to PM me if you have questions.
The owner at Parabellum talked with me about offering a free Glock seminar in the next month or so to talk Glock basics and answer questions like this. I'll post it up when we can get a time scheduled. We're all still in shock about losing Coach but hope to get something going soon.
Anyone in the Indy area can PM me and I'll keep you in the loop about the seminar. It will probably be limited to 10-12 people.
Johnny Glock is really loving the new Timney Alpha Glock Trigger. $150...
Myself, on my Gen 5's, I went with the Ghost EVO Elite connector and a fluff and buff on the rest. Factory springs, other than a lighter safety plunger spring.
Look up "Glock 25 cent trigger job". Many articles and videos on the concept. This and a connector as has been mentioned made a world of difference on my Glocks. Just make sure you polish and don't remove material and you'll be fine.
Going up to a 6# trigger spring helps lighten the pull also. It has caused reset issues in some people's pistol, mine have been just fine. It's very easy to go back to the 5# if you have an issue.
I haven't changed striker springs, just because I like what I have and it runs reliably.