I am literally amazed that you get any channels at all with the antenna that you are currently are using based on the info you posted. If you put that one up in the attic, maybe your reception would improve or at least it would not be so flaky when you move about.
The SquareShooter you are looking at would be throwing good money after bad. Do yourself a favor and get an outside antenna and mount it at the maximum height you can and get it over with.

You can pick up what you need at a HomeDepot, Lowes, or even Rat Shack for about 75$ or less for the antenna, another 15 for poles, 25 or so for the tripod mount and put it on the top of the roof as high as you can easily get to. Do NOT go any higher than maybe 10 feet or so on that tripod, if you are not willing to put guide wires, though. The wind will wreak havoc if you do, so go one way or the other, but DO remember to ground the antenna and the mounts properly.
When you get your antenna mounted, orient it to about 250 degrees and check out the reception on all stations. Move the antenna at about 5 degree increments until you have the best possible reception on all channels. I am betting with a relatively on-directional antenna like the yagis at Rat Shack that about 255-260 should do you fine. You are not in a situation where you have some located east, some west, some north, etc.
As to who to get to install the hardware, if you cannot do it yourself, do you know anyone who knows enough to put the setup up for you? If you have all the hardware on hand, I would be that the D* installer would be willing to do it if you paid him and he has actually done it before. If he hasn't done it before, its NOT like installing a dish, so he could get really frustrated and botch the job, so ask first. If necessary, call the local electronics place and ask them about installation. They may be higher than a kite on the hardware, but chances are they know someone who installs or they do it for a fee.
As to the cost for this, consider this an investment as there is NO WAY IN HELL that D* will ever carry all the digital sub-channels that you can get OTA, they would have to launch a whole new fleet of satellites to do that as subs are popping up all the time. KET has 6 channels available and D* has NO PBS in HD at all, so as long as I want to see PBS, all of it, I MUST have an antenna.
If you have any questions, feel free to ask and hope things are clearer for you now, you have lots of options, loads of them.