Publisher Corvus/Atlantic currently has a bunch of £0.99-£1.49 specials (possibly time-limited and set to expire when Kobo's holiday sale is over on the 4th, or not) on their mysteries and some sfnal and historical books in the UK which you might want to
browse through, including a Tim Powers novel (not one of his better ones, IMHO). And so does more dedicated
sfnal publisher Titan. (Both of them are couponable @ Kobo, which is where I normally buy, but you're using up Amazon credits, so the next coupon contest isn't going to make much difference.)
I think you'd like Tanya Huff's Confederation aka "Valour" novels if you haven't already tried them, a very fun MilSF series with an interesting mix of alien species and cultures, and enjoyable adventures, as well as an ongoing mystery to exactly why they are at war with strange seemingly unfathomable beings, many of whose installments are just £0.99 from Titan. She writes them kind of like a Canadian mix of Bujold and Heinlein. My (brief) thoughts on
#5 in the What are we reading thread.
I'd also consider getting Maureen Jennings' Murdoch Mysteries series of historical mysteries set in late 19th century Toronto, also mostly £0.99 from Titan (in fact, I plan to snap them up from Kobo myself, if the sale prices last long enough for the next contest to kick in). I haven't actually read them, but they're the basis for the eponymous very popular TV show, which I enjoy quite a lot, and she's said to be one of our better mystery novelists.
Titan also have a few Mercedes Lackey and Further Adventures of Sherlock Holmes (the series reprinting the assorted public domain crossover mashups by established writers such as Fred Saberhagen) at that price point, if you're interested. The quality usually varies on those latter, but I've generally found them at least worth a look from the library.
Some quality semi-humorous non-fiction about ancient Rome and Greece by classicist Peter Jones (
Wikipedia) which I recommend (I haven't read these particular ones, but I own and have greatly enjoyed his "Ancient and Modern" column collections, and his excellent
Classics in Translation, as well as his language learning titles, enough that I feel confident in selling these as a blind buy and snapped them up myself during last years' sales) for £1.89 each from Atlantic Books:
Eureka!: Everything You Ever Wanted to Know About the Ancient Greeks But Were Afraid to Ask &
Veni, Vidi, Vici: Everything you ever wanted to know about the Romans but were afraid to ask. He has
a regular column in The Spectator, which you can try to see if you like his writing.
I would also tentatively recommend considering from the £0.99 Corvus sale (I have purchased and started reading these authors, who have good reputations, during previous sales, and so far it's seemed pretty solid, but I haven't finished yet, so I don't know if they fall apart completely at the end):
- 66º North by Michael Ridpath, 2nd in his Fire & Ice series starring an Icelandic-American cop who gets relocated from Boston to Iceland as a cross-cultural crime consultant. We've previously received the 1st-in-series free as an iTunes UK Book of the Week, which you might have picked up back then, as well as some backlist KDP freebies of his.
- 1222 by Anne Holt, 8th in her award-winning Hanne Wilhelmsen series set in Oslo. The other books in the series, as well as Holt's Vik series, seem to drop below £2 on sale every so often.
Another follow-up to a previous freebie you might wish to try is:
- Lucifer's Tears by the late James Thompson, currently just £1.85. This is the 2nd in his Inspector Vaara series set in Finland, of which we got the 1st free. YMMV on this one, as the series is the tale of an increasingly corrupt police officer turning to stealth-vigilantism, and it's kind of on the violent (but not too gory, relatively speaking) action thriller wish fulfillment side. But I really liked all four installments of it and it's probably worth it to read the freebie and decide whether you're interested enough to try the 2nd. My comments on #1, #2, #3 & #4, if you're interested.
You may also wish to consider the exclusive ebooks from Amazon's own imprints, which just aren't going to show up cheaper elsewhere. They don't seem to put them on sale in the UK nearly as regularly as they do in North America, but you might want to keep an eye out for discounts on:
- Martin Jensen's "The King's Hound" historical mystery series from AmazonCrossing, which I think you'd enjoy. They're very fun books set in the Danelaw under the reign of King Cnut, starring an unlikely partnership between a manuscript illuminator and his half-Danish warrior traveling companion, with a kind of semi-antagonistic buddy cop feel. I really like these (my comments on #1 & #2), and future installments are on my auto-buy wishlist.
- Possibly Leena Lehtolainen's Maria Kallio series. This is another auto-wishlist series for me, but I think these would perhaps be less to your taste (they're pretty slow-paced low-key retro-90s Finnish police procedurals), but maybe worth giving a try if the samples read well and they show up on sale. (My comments on #1, #2 & #3.)
- Aaron & Charlotte Elkins' Alix London mystery series, if you haven't bought them all already, since you've enjoyed the Gideon Oliver and Chris Norgren ones you got from Fictionwise.