after having realised how the rear springs on my Octavia are held in, basically the weight of the car. I have decided to change them myself rather than get the garage to do it.

Can anyone recommend a supplier and also does anyone know if there are any parts other than the spring that should be replaced?

See which of the part places are nearest you and go there. Look for GSF, Euro car parts, unipart etc. Chances are they'll all get the bits from the same factories.

just be careful trying to drop them out. my advice is buy a cheap pair of spring compressors and do it properly,jacking it up to twist the axles to full stretch will not do the bushes any good.

plan is to get some spring compressors, just surprised how little held them in, was expecting bolts or something to hold it all together.

Where in the country are you? Until a couple of years ago I ran a motor factors and still get good prices from them, if your near Leicester you could even pop round and do it on the drive – got a fairly comprehensive tool kit including air tools. Shouldn't take more than half hour or so.
Doubt you'll need compressors for rears, just jack the car as high as you can, support on axle stands, put jack under trailing arm, remove shock lower bolt, lower jack, remove spring and as the haynes book of lies says replacement is the reversal of removal. It's important not to fully tighten the lower shock bolt until the car is back on its wheels though.

Thanks for the offer mike i am in either cheltenham or chester, that was one method i thought of, but i figured, and tell me if this won't work. If i jack the car up, then use a spring compressor the spring should come out without needing to touch any bolts.

buy half decent spring compressors if you're wanting to do it your way. Those springs hold a massive amount of energy and if they let go you don't want to be anywhere near them…

Plus you'll find them really handy anyway.

If your in chester try chester exhaust supplies (CES) – not who I worked for but part of the same buying group/trade organisation.
Only problem I could see with using compressors is getting decent safe access past the trailing arm and brakes, normally compressors are used for struts where you cant release the tension with them on the car and have to be fitted evenly round the spring.
Another, possibly easier, way would be – loosen wheel bolts, put jack under rear sill lifting point and just lessen the weight on rear wheel, remove lower shock bolt, jack up until wheel is off ground, remove wheel, replace spring, replace wheel, lower slowly until wheel is just back on the ground, replace shock bolt but don't tighten, lower car, tighten all bolts, repeat on other side.