I went from 3X8 to 1X9 a couple of years ago and life is great! Picked up a discounted Race Face Evolve crankset (previous years model) online and added a Race Face 38T chainring designed for a 1 X setup…not a big deal but chainrings have ramping on the teeth to accomdate front gear changes so it isn’t necessary with a 1 X setup. Your middle chainring right now is probably a 32T (+/-) so the 38T gives me a little more top end while demanding a little more leg muscle on the climbs. That’s easy to swap out if you’re going to ride different trails with more climbs. I did all the work myself and the Park tools I bought more than paid for themselves. The other consideration you want to ponder is a short cage derailleur for the rear cassette. Your 3 X setup probably includes a long cage derailleur to soak up the slack associated with 3 chainrings up front. You dont’ need it with a 1 X setup so a short cage derrailleur will make gear changes really crisp and snappy. This is not a requirement but is the logical evolution of a 1 X drivetrain.Here are my lessons learned and what I did:
1) Race Face Evolve crankset (came with 32T single ring but picked up a 38T single ring for the type of riding I do). Do your research as there are tons of great cranksets–I picked Race Face because of affordability, reliability, made in N.A. and they are EXTREMEMLY easy to install.
2) A chainguide was absolutely essential and I went with MRPs "1X" chainguide made specifically for 1 X setups with a cross country/free ride focus. Works flawlessly. I’ve never dropped a chain on the trail.
3) After riding this way for a while I decided to complete my drivetrain transformation. I picked up an X9 rear cassette (and short cage derraileur) along with the X9 gear shift lever. A 9 speed chain completed the transformation.
My bike is not a "high end" carbon machine so that’s why I went with the componenets that I did. You might want to increase or decrease the quality of your build but mine is a great balance of value and quality.Couldn’t be happier.Good luck!