My good friend David Morgan has just published a SF novel "The Bend in the Sky" which might fill the bill. I know he's an admirer of Terry Pratchett, and has much the same sense of humour, so it might be worth a try.

Details below:
"The Bend in the Sky" by D.S. Morgan
Distributor: *Orca Book Services. Tel: 01235 465521. Email: tradeorders@orcabookservices.co.uk
BIC subject category : FL  Science fiction / FM  Fantasy / WH  Humour…
Paperback 224PP 216x138 mm Portrait
ISBN 9781780881614 pb / 9781780881621 hb