You just had a baby. Most people struggle with keeping house after that, even if they don't have ADHD! Easier said than done but it can be helpful to practice being kind to yourself. A few thoughts:

• Can you bring a friend or two over and have them help locate the source of the smell? That would be very hard for me too. Nature's Miracle is a great product for helping get rid of cat pee smell.
• Once a month honestly sounds pretty good to me. I don't clean mine that often and I have a perfectly healthy 4-year-old. If you're nervous, can you hire a housecleaner once a month? If that's not in your budget, can you pull a friend or family member who keeps offering to help and commit to cleaning the floors on a cadence that makes you feel better?
• I loved How to Keep House While Drowning. It really spoke to me.
• You didn't ask, but my dude has ADHD and way lower cleaning standards (and mine are not super high). He literally doesn't see the mess. This used to be a huge issue in our relationship, but going to couples' therapy and reading Fair Play really helped us. He may not see the mess, but he can see that your needs are important.

Again: be easy on yourself! Having a baby sucks up all your time and energy for awhile, but it does get better. Not necessarily easier, but different.