The Tough feat is exactly what you want.
Your hit point maximum increases by an amount equal to twice your level when you gain this feat. Whenever you gain a level thereafter, your hit point maximum increases by an additional 2 hit points.
On the other thread, plenty of people gave you advice on increasing your constitution, which is also an option with feats, but if that's your goal, it'd be better to just use your ASI on level up instead of taking a feat.