I always have a top shot of mono (maybe like 2m in your case?). If you just do a bimini to a gt or albright then you should be right for tieing your mono to swivel. this will also give you more abrasion.

I recommend using the swivel. But yeh, uni shouldn't really slip. Maybe try a clinch knot, if yours are slipping.

Both! There arent a lot of knots that work well for braid to terminal tackle. Braids just too fine and slippery for most knots that were designed for mono. If you really want, you should use an improved trilene (go 8 twists up, 6 twists back if you can), or better yet, a bimini to multiple cats paw.

If you can though, running a leader to your braid would probably be a better idea for a few reasons. With a good knot, it will be stronger than your existing setup, will have better abrasion resistance, and easier to cast (if you remove the swivel). You can still tie the leader to a rig via a swivel if you want though.

I use GT's for pretty much everything. They arent quick to tie, but they arent that hard once you know how and they'll last for ages (multiple fishing trips). Otherwise a properly tied improved albright. Although I hate them, a uni to uni knot with the braid doubled up and enough turns will still probably be stronger than your current setup.

Also, sometimes worth trying out knots at home. Get some scales (or a weight) and see how your knots hold up.

pity about the big fish . imo you should always use a mono shock leader and never tie the braid straight to swivel. look up some of the knots for braid to mono on line or do a search on here, always plenty of talk about what knots to use.

i only use a swivel to basically stop my sinker running to my hook would i be better of letting my sinker run to the hook or is there another way of stopping it?

Mate I use the polmar (doubled) from braid to snap swivel but pass it through the loop twice before taking it over the swivel then pull it all back up on it's self. Never had it fail on me with up to 14kg Dhuies, Double header pinkies & 30kg sambo's. I always run a swivel at the top of my leader & have the rigs just long enough that the sinker is below the water line of the boat with rod in holder.

i did that today the double polamar seems pretty strong  i will test it out friday then if not try some of hlokks ideas cheers for your help crew

As I have been too lazy to learn new knots and I'm always in too much of a hurry to get my line in the water, I normally fish with a uni knot to a swivel on braid. I know this is not ideal and in the early days I had a few knots give out. However have had no dramas with the knot as long as there are at 10-12 turns (I've pulled in a couple of bloody big rays and the knots have held).

That's on 80lb braid though...I doubt the knot would hold out to anywhere near breaking strain so would recommend the mono leader discussed above.

IMO don't tie straight braid to a swivel, hook etc because the knot will give way.

I use a double uni to join fluro/mono to braid, I do 5 or so turns on the mono and then do double that with the braid, and have never had it give way when fighting a fish/snag 

I always tie braid straight to the swivel with a uni knot, with twice or three time through the eye and 7-8 time through the loop. Never had one fail and have never learnt to tie mono to braid because I've never needed to.

I just use the good old granny knot for bgraid to swivell..  On 30lb fireline to swivel double up the braid and just tie your granny knot.  Never had a braid to terminal failure yet.

Even up north with a triple header reds all 10kg plus knots never budged.. 

Then I just run my bottom basher gear from there about 2 meters of 100lb leader with dropper loops.

like chookc said a basic knot but me and my mates burn the tag  end of the knot, he has gotten sharks and rays up north with no braid to swivel failure.