Where can I find netherite?
I have been going at this for an hour and I have found only 3 netherite scraps. Are there certain coordinates where I should mine?
What's the most efficient way to mine in the nether except beds?
The best place to mine for ancient debris is at Y level 15, although you can find it anywhere between Y=8 and Y=22. Source: as usual, the official wiki.
I dont't think biomes make any difference for the ancient debris, but netherrack is much faster to mine than basalt or blackstone, so it would be better to mine in netherrack areas.
As for the best mining strategy for ancient debris, it's strip mining with TNT. Beds are actually the worst possible way to go. You can check Cubfan135's video where he tried all the different ways. It was for Java edition so the results might be a bit different for Bedrock.
Of course, if you are interested in the other resources you can find in the Nether (quartz, gold, blackstone...), then just strip mine with a good pickaxe and patience.