two ways to approach it:
if you really fancy doing an overhaul and going 1×11 and your 9 speed kit has life left and has value then sell it before it’s fit for the bin to help offset the cost.
Or
if your 9 speed kit is shot then do it anyway.
To keep cost down I would go SLX RD and possibly shifter (don’t actually like my XT 11 speed much). Cassette wise I would either go Sunrace MX8 or XT. You could go sram if you can get an XD driver for your hub but that is extra cost both for the driver and cassette. Also if you have 104 bcd then going for a 46T cassette means you have better front ring options as you can only go down to 30T round and 32T oval on 104 bcd.
I would go 32 or 34T oval ring, I run 34T oval on my 26″ hardtail with an 11-42T cassette (46T wasnt out).
Ring wise try oval.