Yes - you can use an AIO (all in one) for the CPU while leaving the rest of the PC air-cooled. Here's a link to some: (PCPartpicker AIOs)
There are 4 groups that people usually choose from - 120mm (1 120mm fan), 140mm(1 140mm fan), 240mm (2 120mm fans), 280mm (2 140mm fas).
The larger you go, the better cooling capacity and noise you'll get. Most people go with 240mm.
However, I'd really recommend a high-end air cooler (such as the Noctua D15 or the Dark Rock Pro 4) - they'll be quieter (while being cheaper) and cool about the same as a 240mm AIO. They also last longer and still passively cool a fan breaks (compared to an AIO where if the pump dies, your CPU will slow down as far as it can).