[Pulpmeister]

On the OP, I think the right way to look at it is like this:

"I don't use single quotes."

That's a sentence.

"I don't use single quotes," he said.

That is a single sentence, not two.

If you treated the sentence within the quotes as a complete sentence in example 2, you would have to go like this:

"I don't use single quotes." He said.

Which is seriously nonstandard.

The quotes are there to distinguish speech, that is all. If you used a more European convention, e.g. the dash, to serve the same function, you get (and I don't know how to insert an em-dash):

--I don't use single quotes, he said.

Which is quite obviously a single sentence.

All you have to do is keep it clear and unambiguous. The normal typographical convention is the comma within the closing quote. Best to stick to it.

On double v single quotes, I rummaged up the oldest UK printed hardbacks I could find easily in my, er, Library.

Ten Trails to Tyburn, by Bruce Graeme, published by Hutchinson during WW2 (Book Production Economy War Standard): double quotes.

Master of Ballantrae, R L Stevenson, Collins' Clear Type press, undated, but from typographical and other considerations certainly around 1900, also double quotes. And, just to make life more fun, the double quote with a space:

" I think you are a devil of a son to me, " cried his father...

instead of

"I think you are a devil of a son to me," cried his father...

There's also a curious inconsistency in-house. Penguin Books' first P G Wodehouse paperback, My man Jeeves, has, in its 1936 reprint double quotes (with space!). But in a late 50s Wodehouse Penguin, not the same title, I find single quotes (without space).