You should get one of the big 3ds or stylized pen stylus . Because for the non nintendo styluses tend to be bigger. An if you do digital art a pen stylus might be useful.

Good for You! I bought mine on Aliexpress. It's on telescope so it's fit perfectly in slot but it's possible to extend it for better use.

I just got some random ones on Amazon. Color matching for my New 3DS XLs and random color ones for my original 3DS XL.