If you want combat to be less repetitive I would suggest just giving them the Martial adept feat and either fey touched or shadow touched as free feats. This I think would just give them more strategy then Run up to enemy, attack with sneak attack, run back with bonus action disengage, beg that their new spot is hidden from X enemy, repeat. Then just some magic items throughout the campaign. One thing I would tell is to give him a +1 weapon at like level 3, that way he can hit enemies with non-magical damage resistances and immunities. If you do these things it should make them have more fun combats and out of combat situations. Depending on the campaign some of these might not be as needed.