On the topic of travelogues... have you read the Provence books by Peter Mayle? Really good. (I'm a foodie, so food travelogues are much more my speed, lol!)
On the mystery front... I love Sayers, also love Marsh, am working on Allingham, and eagerly seeking other Golden Age/Golden Age-style authors, so recommend away!
Edmund Crispin is one I like very much.
And Patricia Wentworth is fun, as long as you don't read them one right after the other. The "formula" shows a bit too much if you do that.