Stitching Needles are another rabbit hole to disappear down!
Not all needles are the same -- Harness needles are rounded, less sharp than glovers' needles, for example. You don't push harness needles through leather to make holes, like a cloth sewing needle, so they don't need to be sharp.
John James needles get consistent recommendations, and I must concur -- they are good quality.
The difficulty is knowing which ones to get-- per their website, they offer the following for Saddlers Harness needles:
25 Saddlers Harness needles in paper envelope.
Size 1 54mm length x 1.02mm diameter
Size 2 54mm length x 1.02mm diameter
Size 3 54mm length x 1.02mm diameter
Size 4 48mm length x 0.86mm diameter
Size 18 (1/0) 57.5mm length x 1.09mm diameter
Size 17 (2/0) 59.5mm length x 1.42mm diameter
Size 16 (3/0) 61.5mm length x 1.63mm diameter
And now the beginner is hopelessly confused -- why so many? which ones do I need? what thread thickness do I need? flat braided or round twisted? polyester or linen? etc.
It depends on the project: what weight or thickness of leather, which also dictates thread thickness and stitch spacing. Then you can figure out what needle would work.
People (not me!) who specialize in sheathes and holsters can help you figure out those variables if you ask on the forum.