Little Details

Context: 

Fanfic, set in the British Regency, slash pairing, letters between a gentleman and the man he sends out to buy books.  The gentleman is well-off, and the man is from his household, so there isn't an issue with costs for paper, ink, or postage. Neither of them are at all overtly sentimental,  and I love writing covert-declarations-and-bawdy-insinuations-between-the-lines stories. 

Search terms tried and what I've found so far:

"Regency letter-writing", "letter-writing in Jane Austen's time", "nineteenth century business letters" "Regency business letters" (even if I do an exact string search for the latter I'm not successful)

Conventions of writing, crossing, addressing, payment by recipient--interesting as far as it goes 

Physical visual examples which I can find on the web might be ideal except that I can't read whatever hand they wrote (copperplate?) with the ink faded in a tightly-packed and sometimes crossed format. 

Because there's so many people writing Regency romance after the style of Austen or Heyer, and because there's a lot of people wanting to write letters of consequence (and a lot of remaining letters written about big events) there's a very strong preponderance of detail involving letters about feelings or major events. I'm really looking for the opposite of that--the appropriate Regency style, but something dull I can mess about with.