What do you mean by the boat is "giving you trouble".
I'm about 5"10-5"11 (I think) and weigh 78kg's. I recently went from a Riot Disco which I got for cheap to learn a bit on. It has 189L volume, and I couldn't get it up on the nose or the tail in the flat. I found it quite hard to throw around.
I just got a Jackson All-Star which has a volume of 197L. That's an extra 8L on something I couldn't throw around at all. After getting the trim right on my kayak (moved seat back a little to begin with, ended up re-doing happy feat and getting the seat a fair bit further), I am able to consistently get up on my tail without much hassle, and am very close to getting up on my nose. I know I'll be able to get up, but I have very bad technique at the moment. My mate who probably weighs less than you and is smaller had a go and could get up on his nose no worries.
This boat has heaps of room, but due to the design of the kayak, it is easier to throw around than my previous boat which I found very hard, even with MORE volume.
I'm not trying to sell you into a specific boat (I love the design of my new jackson, but have a few question marks on the durability of some of the outfitting, which I'll be emailing jackson about), but I'm just trying to highlight the fact that it's a lot about a boats design, not just fitting into the smallest boat you can. I've also had a quick go in a Dagger Crazy 88 and seemed to have plenty of room and loved it. Quite easy to throw around. Try and demo some boats if you can, hopefully you'll find one that you fit in well, and has a good design so you can still throw it around at your weight.