24f:36r would be a little bit lower gear at the bottom end (0.66 ratio vs 0.6875 on your 3×9)
You won’t get smaller than an 11 on a ten speed cassette, so to have the ‘same’ ratio on a double crankset you’d need a 44T ring. Which won’t work, as a derailleur can only do 14T as a difference. But, how often (really) do you need your biggest gear ratio on 3×9?
So – if your needs are for the same at the low end and you can give up top end ratio, and assuming an 11:36 cassette as opposed to going for fancy 40T or 42T aftermarkt solutions, then I’d say a 24/38 double.
If you can compromise a bit at the low end, then a 26/38 or 26/40. But i don’t know if you often get 26/40, they’re usually 28/40.
I’d suggest 26/38; that’s slightly harder at the lowest end (0.72 ratio) and at the top end you’ll have 38:11 i.o 44:11. But 38:11 is almost the same as 44:13 so in effect you’re only losing your very top gear.
And yes, if you’re on a 29er, then the gearing comes out about 10% harder than the same combinations on a 26er once you account for the difference wheel size makes on the total gear inches.