I recommend a Snail 30t or 32t and XT 11-40 or 42, or for slightly cheaper (possibly more available) the Sunrace 11-40 (or 42), both cheap off ebay (or other cheap brand). I've got a Snail 30t on one bike, and 32t Deckas on my kids old hardtail, both work fine. The 30t has threaded bolt holes, which is kind of cool, so you just need the bolt side of the chainring bolts. You can go pretty fast with a 30t front, if you're very fit and racing on a lot of gravel roads, you might need a 32t, otherwise a 30t is big enough for nearly all mortals on a 29er.
There's a couple of Sunrace models, just like with shimano, the more expensive ones have a large block/billet spline for the bigger cogs, which won't bite into your freehub like a cheaper cassette, especially if your freehub body is aluminum you'll want to get a better quality cassette. I've got Sunrace on a couple of bikes (for me and my kid), they have held up well.
Check for chain wear, and probably just put a new chain on the with the new stuff to avoid premature wear.
Option 2, keep it as a 2x: If it's mostly just for clearance over logs, you can just ditch the big ring for a 'rock ring', and keep it as 2x and think of the small chainring as the 'bailout' for steeper climbs. My hardtail was 3x, I had a race coming up with a lot of logs and I didn't want to destroy the big ring, so I replaced it with a rock ring, and realized that even for racing in cat1 I didn't need bigger than a 32 front. I left the front der on that bike, and I've switched it back and forth from 1x9 to 2x9, 2x still has a place in this world.
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