Hi Stephen,
You might be in luck - I am also having major problems looking after invoices, accounts and that sort of thing.
A have a couple of guys that do a bit of work for me and one has just in the process of building mine.
I can let you have a sneak peek, to see if it is the sort of the thing your looking for.
Its all server based - so you can access anywhere.
Pm me if you interested.