Wow. Where to start? There are so many options. How do you like your kit now? If you want to upgrade, an ego would provide longer battery life, and also allow you to use an LR atty or carto (warmer vape that simulates a higher voltage vape). You should also be able to almost double the amount of juice you are getting for that price- along with increase the quality if you try some of the vendors out there. A lot of vendors do samples and smaller bottles so you can find something you like quicker and more economically. The vaportalkstore has some great juice, vermillionriverejuice has free samples if you pay shipping (and I can vape this all day long), Boba's Bounty from AVEJuice is very popular, also check out guidetovaping.com for a changing list of popular juice vendors. The VT forum here is invaluable- poke around and learn, or ask questions here and you'll find the cure for your vaping ailments.
I don't use cartos, but a lot of vapers rave about the dual coils. Someone will be around shortly to chime in on where to get the best deal on cartos.
Good luck, and welcome to VT!