Hello!
Sorry it's been so long. I got totally stuck on the high side driver, and after months of searching and trying things with mosfets and stuff I lost interest and banished it to a cupboard.
Recently I was pointed to a website called http://ruggedcircuits.com/ which has a schematic for a high side driver.
I've ordered the parts and spent this evening bread boarding them and confirmed that it will work for what I want! Really pleased. Big thanks to rugged circuits.
I am currently designing the PCB in eagle, and this should be finished soon. Then it's off to veroboard for prototyping. I had to make some changes to the sensing side of the circuit, using optoisolators. This is yet to be tested, but I'm confident about it.
So all in all, I hope to have it prototyped in a couple of weeks, a bit of testing, and then a PCB made. Can't wait.
Watch this space :)