Adding tv in bedroom

[Pickup jockey]

Hi, Looking to put a tv in front bedroom in a Eagle ht 27.5 bhs. I see that they tell you where the wall will bear the weight. But I noticed that the shower is on the other side ! Since I want to put the longest screw possible and not put in a couple of back scratchers in the shower has anyone have an idea what is a safe length of screw? Some one must have done this project and save me from repeating a mistake! What size tv would be a reasonable size? Thanks