first don't listen to the kid with a pic of himself, he is only 13 and has tried to tell a guy he couldn't surf fish for small sharks with a 7 foot ugly stick medium action which i know you can, second like the first two guys already gave you the best advice but to add to it check with your tackle shop to see what they would recomend and go from there, they should be willing to help out or just go to the line isle and find your favorite line in 12lbs test and check the diameter, it is marked right on the top with the name and line info and then take it to the braided line and find a quality braid around the same diameter. and all test lines in different brands are not always the same diameter, it depends on the maker, the process and the fish it made to target. cajun red line in 10lbs test is not going to be the same diameter as a 10lbs test fly line or even trilene big game 10 lbs test. but yes when you buy braided line get a quality brand not a cheap one-you do get what you pay for you know and yes make sure your rod and reel can handle a braided line, for this check with the manufacturer and/or your tackle shop.
it also would help if we knew what you are targeting, there is no need for a braided line for trout.