Your 'other friend' is right. Flare jeans and boot-cut jeans would be best. They make your legs look the longest. I suggest getting something high-rise or regular, definitely NOT low-rise because it'll make you look short.
And if you want to get something skinny, you can, but not skin-tight or clingy. This will still flatter your shape while at the same time not giving too much curves, which make your legs look shorter.
The most important thing, though, is to go for a wash that is just one straight color all the way through. If there is any color differentiation on the jean, it will make you look curvier, not skinnier. The key is to get a very plain, basic jean with a specific wash used throughout without any fading anywhere.
Also, try to get them without buttons or any detailing. These, again, will make you look curvy.
Color-wise, go for a super dark wash. Just as black makes you look skinnier, the darker your jeans are, the longer and skinnier your legs will look. Don't go for light-wash jeans, they shorten your legs. What you want is something elongating, and dark wash jeans are just that.
And one last thing: DON'T listen to all of the people above who said to wear jeggings! This is the exact opposite of what you should do. Jeggings are a very good example of what NOT to wear to make your legs look long! They make your legs look short and curvy, which isn't what you want at all. So just ignore those people.