When you say the windows AC are "getting a bit much" what does that mean exactly?

(what is it that you want to avoid or want to do better?)

Most split systems are placed on the outside wall, because that's easiest. You can put it other places.

The advantages are that it's very efficient and you can only heat/cool the rooms you need to since they work independently. So, for example, you might cool the bedrooms at night but not the rest of the house as much.

The big drawbacks is finding someone who knows how to install them and that the wall mounted units can be ugly. (There are other options for the indoor unit also).

Thank you! The ”bit much” refers to my aging hubby having to haul the 4 units in and out of the windows every year and them store them in his garage. Also cleaning them out due to dirt and mold yearly.

We currently have one large unit in the den and two bedroom units that make our entire home comfy. (other unit is in attached apartment)

Im thinking at the very least getting a split in the den. It could be on an outside wall but it woild be less conspicuous on the inside wall .

Okay, that's a little more clear.

I assume when you talk about "split unit" you are talking about a mini-split ductless that look something like this the example below.

Note that you have one compressor outside and multiple individually controlled units inside.

Consider replacing all of your window AC's at the same time. I'm not sure where you are, but these generally provide heat also (they are a heat pump).

You can put them on any wall, but you have to get the refrigeration line set to them, power, and a drain. You mount the indoor units high on the wall.

You can run the line sets through the attic, for example, but the drain can get tricky on an inside wall.

You can also get indoor units that are recessed ceiling cassettes or concealed ductwork.