Luke, you will be fine with a floater and a six weight outfit so long as the weather is kind to you. If there is plenty of cloud cover the fish come very close (even as close as a yard out) and you can catch happily on a floater. It's only if you get a clear day or a very windy (or freezing) day that you will need to go very deep.
First thing you have to work out is how deep the fish are - if there are plenty showing then a floating point fly and a couple of buzzers or nymphs will keep everything in the top two feet, where they are feeding.
If there are none showing I would aim to cover all depths with three buzzers or nymphs. If it is windy, space them at 5ft intervals and just retrieve very slowly ("straightlining"), if it is relatively calm fish a bung with buzzers at 4ft intervals to cover all depths.
Personally, I believe a bung rig will usually outfish the straightline rig if the conditions allow you to fish it OK, but others would disagree, I am sure.
If it's bright sunshine, you need to go and buy a Di7 shooting head
Good luck on Sunday,
Charlie