Anyfish - to get you going waders are fine. they are the same as bib and brace kayak trousers. In fact, I don't buy breathable waders anymore, because for what they are they are TWICE the price of breathable paddle pants, which I then use as waders. Turned things on their head. Use paddle pants (the Palm Sidewinders are what I use - had this pair 6 years now, breathable, bone dry and have a pee zip included and built stronger than Simms at £500 - for £200. best wading secret for anglers out there!)
If you intend to use your waders, you will wear them through in a very short space of time - on the backside, or go through the knees where they rub against whilst you are sat. If using "open" topped chesties, then just put a wading belt around them. Paddle pants are tighter fit than most waders, which limits the amount of water that gets in, it seeps in, rather than fills up. The paddle pants will brush off brambles too - something breathable waders won't do, they don't have the reinforcing the paddle pants have.
There are two sets of gear you really need. For summer a lightweight outfit (in really warm weather a rugger shirt and shorts and plenty of factor 50 - you will get burned to a crisp if you don't prepare against the sun.
Winter and spring. This is when the water is at its coldest and you really must not take short cuts at this time of year. A breathable drysuit seems expensive, but it will last 10 years if you look after it properly. The protection a drysuit offers is unmatched by anything else. Remember though, a drysuit offers NO INSULATION PROPERTIES WHATSOEVER, like breathable waders, you have to supply the warmth in the form of undergarments. Insulated base layers are good, for very cold weather a fleece romper suit is the norm. You need GOOD under layers too, because paddling makes you warm, and if the sweat is not wicked away efficiently you will then freeze when you stop and start fishing. It is worth paddling at a lesser rate in cold weather to prevent the warmth building up too much for this reason.
Before you even start to fish, have you learned how to rescue yourself yet? If you go in, do you know what to do - and have you practised it so you know you CAN do it for real. In an emergency situation (you in the drink IS an emergency situation) you will have a maximum of 3 attempts to get back on the kayak - every time you fail increases the chances the next attempt will fail. After 3 attempts you will have used so much energy and your morale will have dropped ensuring any further attempts also fail. Learn how to do it, do it right and do it first time, every time. The Loghs Agency are looking at setting up a scheme with kayak angling instructors. i am the first qualified Level 2 kayak angling coach n the country - but I am in Staffordshire and cover this side of the Irish Sea, so no use to you until i am over in the spring to Coleraine - just before Easter. If you want to come to the river there I will happily go through the mechanics of kayak fishing with you. I will soon have a coaching page on my website -
Kayak UK - home of Kaskazi Kayaks in the UK have a look through the forum and the gallery.
Some fly fishing from the kayak pictures: