I need a new air filter ASAP

I must admit that our wife does way more around the house than I do.

Of course, I do lots of housework and laundry and cleaning.

But my wife Jill does all of the home improvements and all of the repairs around here. For instance, Last week our air conditioning stopped working for some reason, then there was just warm air coming out of all the air vents and the apartment just wasn’t cooling down, but we had the air conditioning turned all the way down on the temperature control, but nothing was happening. So Jill went down to the gas furnace room in the basement to see if she could figure out what the issue was with the air conditioning… I heard her messing around with the central air conditioning in the basement, however there still wasn’t any cold air coming out. Jill called up the stairs to get me to come down from the kitchen. I went downstairs to the gas furnace room and Jill was holding up a gross looking air filter. It was gray with dust and dirt and it looked like it was completely clogged up. Jill said that it was no wonder that there was no cooling going on with our air conditioning unit, but she wanted to work on cleaning out and blowing all the dust and dirt out of the air conditioning system and so she wanted me to go to the hardware store to pick up a new air filter for the air conditioning unit. I left to go to the store, but when I got to the HVAC aisle, I saw that there were hundreds of filters that would fit our air conditioning unit. I had no idea which air filter to get.
Ductless multi split