The C5 2.2hdi can be auto, as is the 2.2hdi 607.....
Just to broaden your search really...
2003 2.2hdi estate - mine 1998 Volvo 940 auto estate - also mine 2019 Citroen C3 something - the wife's PP2000 user, can help with faults / diagnostics in the Bournemouth area.
The 2.2 is a great engine, but is let down by a very complicated vacuum system which, due largely to its size, is prone to leaks, and by the particle filter system which was PSA's first attempt and didn't go well.
There is a lot of expertise on diagnosis and repairs at large in the community here and on similar sites. I think it's just a case of knowing what you're getting yourself into.
On the later 170hp 2.2 HDi the issues -- with the DPF at least, time will tell with the vacuum system -- seem to have been resolved.
The 110 is definitely the sensible choice. Unlike many DMF implementations those on the 110 don't seem to have a short lifespan compared to other models (i.e., the 90) in the range.
On to autoboxes: isn't the AL4 a notorious piece of junk?
IIRC the V6 has a different box, but ServiceBox says not; does anybody know what's what with these?
To get a better autobox might it be better to look at 607s or 407s?