I found this A/C that looks like it would fit your vertical sliding window:

http://www.homedepot.com/p/Frigidaire-12-000-BTU-Window-Air-Conditioner-FFRE1233Q1/205089573.

Your horizontal sliders are too short for a casement unit, as you know.

Don't get a portable A/C unit, you will not be happy with it.

If you have a bigger budget (several thousand installed) and want to keep the windows free, there is something called a ductless split air conditioner, also called a mini-split. You have a unit on the ground like a central A/C but there is a single unit on the wall which distributes the cool air. Here is a link:

http://www.mitsubishicomfort.com/products

Thanks for looking. The minimum width for the Frigidaire is 23", and my vertical window is only 20.5" wide, so that won't work.

With the mini-split, what is the cost of the unit and of the installation? Do you have a HVAC person install that? Handyman?

If you get imaginative, you might be able to get the Firgidaire to work. The width of the unit is only 19". I think the minimum width specification comes from mounting those accordion folding sides that you see on window A/C used to close the gap on a wider window. Take a look at maybe just using one side, or maybe foam insulation stuffed in instead of the sides things.

Mini splits are a HVAC contractor item. As I said, it will cost several thousand including installation. If you have the budget and want to go that way, get a few quotes.

Also, what kind of heat do you have? An interesting twist is that some mini-splits can be used as heat pumps as well, which could be a considerable savings if you have oil heat.

Maybe creative is worth a try, plus maybe trying to find someone to help me with the install (which might be necessary anyhow; those things are heavy).

I have central heat: natural gas.

If you have a little carprentary savy cutting a hole through wall holds several functional advantages over window mounting.

I do not have carpentry savvy; I have to figure out how to hire it when needed.

In a hot humid SW WI I cool over 650-sf 1937 house with a lot of windows perfectly with a Half-Ton window A/C. I use a 20" floor type wind machine fan to circulate the air through the rooms.

Doubt you need a Ton unit.

Your questions are #1 "Are there other solutions out there that I haven't found yet? And #2 " Should I call in a HVAC professional?"

There are dozens of solutions out there but if you have no mechanical skill,why do you ask? Just hire somone to take care of it. Should you call in a HVAC professional to search for a piticular size unit? I wouldn't unless you simply don't want to bother searching yourself. You present a difficult situation for us to offer advise on.

Do a whole house 'free' online load-calc & get others to help you do it.

http://www.loadcalc.net/

Everyone can use this free load-calc & everyone should use it.

Thanks for the responses.

If you don't know the market, it can be hard to know what the correct search terms are. It can also be difficult to hire help when you don't know what you need, you are vulnerable to being upsold or sold something that is not fully appropriate for your needs. Web searching can only get you so far. I've learned some things from the responses here.

My current top contender is to get the Frigidaire and then try to find a handyman/electrician to either help me install it in the existing window or look at cutting a hole in the wall.

A mini-split can be dramatically quieter than a window or hole in the wall AC unit, you can also put in multiple air handlers running from one compressor to have, for example a zone in the bedroom and one in the LR that you control separately. Much more expensive, but the benefits are pretty substantial as well.