@NickP - Firstly, sorry to hear the stress you're under. But believe me, you're one on many 100's of thousands likely affected in the changes over the last couple of years. Best of luck in getting through.
Folks I've seen who got by did the things that Netmeg suggests. If you have the margin to successfully advertise profitably through PPC I'd suggest you take the plunge. Not everyone has that luxury though.
My thoughts are that your disavow file preceded a problem that you recognized was going to happen anyway. Is that correct?
As folks here say, disavow files take a long tome to work their way through Google's system. If indeed you did enough. Also disavowing links may cause a further future drop before you turn the corner with new links.
Something else is in play - why don't you get some inputs by having your site reviewed here : [webmasterworld.com...]