Only Cat vs 2

We have a 4yo scottish fold cat who has been with us since he was a baby. Ive read that its always good to have another cat so they can entertain each other. He has constant entertainment as theres a lot of birds right outside our place and he probably spends 3 hrs of his day bird watching. I also wfh. It seems to me that his fine and never acts like he’s sad or alone. My husbands coworker is rehoming his also 4yo female cat, a tuxedo which is my fave cat. I am very torn if I should get her and worried my other cat would hate me. Any words of wisdom from multi cat parents?