Tom Cox's book is an excellent place to start, although as good as it is, it does not cover the full range of options. Your space is limited, so I agree that slower growing plants would be best. Here are my thoughts:

Spruce:

1. Picea orientalis is the best spruce for our climate, and there are a number of smaller cultivars. There are some yellow varieties (including the famous 'Skylands'), but no blue ones.

2. Picea omorika is considered the next best, although I haven't had as much luck with this species. It's a beautiful spruce, though, and most cultivars have two-toned needles. There are some blue/silver blue cultivars, and many of the cultivars have sculptural appearances.

3. Picea abies does better the further north you go. I have found that the "yellow" varieties do not hold their color well here, and most end up green by late spring. There are no real blue cultivars. P. abies cultivars come in every shape and size.

4. Picea pungens will do okay for a few years, but almost all of these eventually decline. You might get lucky with one that makes it longer, but I can't recommend these plants in Georgia. That's sad, because they are often the best choice for a truly blue plant. If you must try it, garden centers, unfortunately, have no problems stocking these, so they are easy to find.

Firs:

1. Abies koreana is one of the only non-native firs that I would try to grow on its own roots in North Georgia, and you have a better chance of that the further north and higher up in elevation that you are. Fortunately, it's a beautiful fir with numerous fine cultivars.

2. Abies fraseri is almost native, but I wouldn't try it without firma rootstock. There are a couple of smaller cultivars.

Pines:

1. Pinus parviflora is a very nice option, with a great many small and interesting cultivars, including some with yellow and blue highlights. On introspection, I might even be fond of P. parviflora, which is saying something since I really don't like pine trees. P. parviflora do very well here in north Georgia.

2. There are a host of other pine species that will thrive in here and are far superior to our native loblolly. I just haven't experimented with enough of them to recommend them.

Hinoki cypress:

These conifers do very well in north Georgia, and, like Picea abies, have a huge range of cultivars with various shapes, sizes, and colors. True blue cultivars don't exist, although several have a "blueish" tinge. I get overwhelmed thinking about all of the Hinoki possibilities for your space.

Cryptomeria:

If there is a bullet-proof non-native conifer, this is it. There are a bunch of fascinating cultivars, although your color choices are usually green and light green that some pass off as "yellow-ish." You can go from conventional Christmas-tree shape to a cultivar that looks like a Medusa's head.

Junipers:

The possibilities here are also endless, and many do just fine in north Georgia. I don't have a lot of these, but many of the cultivars grow quite low to the ground and are good for tucking into spaces around mailboxes. They can grow quite large laterally, however.

And, of course, there are a ton of other options. I would really recommend visiting a high-end local nursery and seeing what they carry. I can't remember how close you are to Cashiers, NC, but if you have some time for a road trip (and it sounds like you may since you don't plan on planting until the fall), visit Chattooga Gardens. They don't have much in the way of Cryptomeria, since cold hardiness becomes a bit of an issue that high up in the mountains, but they have plenty of the other things discussed above. If you have additional questions about something you see, I'm sure people around here will be happy to provide their opinions.