When I started learning I used size 7 needles and that was when I was about 7 or 8 years old so they're pretty easy to use. I now use size four and they're not difficult either. Wool wise I would go with something easy like 8 ply. Tis is easily available and cheap and is also recommended for a size 4 needle.
As for an easy pattern I would suggest youtube for a few easy videos to learn from. From there maybe try something simple like a scarf to get your stitches nice and even and go from there.
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