Alternating pastel or softer colored art puzzles with vibrant photography based puzzles like this one gives a good variety. Amazon link: RoseArt – Kodak Premium – Colorful Montreal Doors – 10000 Piece Jigsaw Puzzle
Note some of the doors here are repeated – the yellow ones in the second from the bottom row left are also second from the right on the top row – something I didn’t notice until I got well into it but wish I’d noticed sooner.