I have to agree with Dave - 11-36 works like a charm, gear spacing is just right. A 11-40 cassette just works OK with the B-screw screwed in all the way or using an even longer replacement screw. I also tried an 11-42 which didn't really work well.
AFAIC the issue with the wide range cassettes reg. 9-Speed is that they have the cassettes but there are no (Shimano) derailleurs to shift it. At least not out of the box. You could try a Shimano 10-speed derailleur and if it doesn't work ok (which it likely won't), try tweaking it. There are howtos online with re-routing the cable for a different pull ratio. 11-speed derailleurs might be too narrow, chain-wise. You could also use a Sram 9-speed shifter with a Shimano 10-speed derailleur.
Trouble is, all of these solutions are rather expensive if you haven't the parts in the spares box. Rather than spending that much money on an exotic 9-speed solution that doesn't get better over time, invest it in a Sunrace 11-speed cassette and Shimano SLX derailleur plus shifter.
What you don't want is a solution based on hanging your derailleur lower and the Wolf Tooth link extensions don't work with 9-speed derailleurs. I tried it (and it's rather expensive too).
Best to stick to inexpensive 11/12-36 and a 30 or 32 NW chainring. Or try the 11-40, but that's the max you will be able to get working properly.