Found this pic. done by a decorator, different patterns and it WORKS...as long as you bring in your other colors loveseat blk. chair etc. and stripes are cool, modern etc.
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You have a lot of straight, contemporary lines so I would keep going with that, but I'd use a couch with a few distinctly different details so you don't get that "tried to match but missed" look. For instance, continue the squared arm, but look for a lower arm that isn't full-depth like the loveseat - for instance, Pottery Barn's Seabury (actually I like the dark wood frame and flared legs on that one, which would tie back over to the bookcases) - or a box-style arm/back like Crate & Barrel's Presley which also has that nifty wood frame. Mitchell Gold's Fred couch would be a really awesome transition between the Eames chair and the existing loveseat, with the square shape and tufted back, if you could find some way to keep the Eames chair in the room. Make sure the scale of the two pieces is the same, paying special attention to the seat height - it looks kind of weird to have one seat significantly higher or lower than the other.

I think a low-to-the-ground (very short legs, not low seat) style would work better than a skirt if you want a less "leggy" look. Ikea's Karlstad doesn't look bad though, and would be an option if your budget is so tight it squeaks. ;-) The long cover seems to only come in white but you might find a great fabric cheap on Fabricguru.com or eBay and have a replacement cover sewn up using the white one as a pattern.

You're not confined to a print unless you want one, but if you do want to go that way I'd look for something in a Deco or Mid-Century Modern style, either very subtle or strongly graphical; but I think a compatible solid in a heavy brushed canvas or twill would be just fine, especially with pillows that bridge the colors. Leather is also an option to consider, if it's in the budget. (If you were keeping the black Eames chair in the room, this black/beige print would be too cool.)

BTW, if I may make an unsolicited comment, the pillows on the loveseat are a little traditional in style for the rest of the room, which skews contemporary. A more modern pattern like C&B's Spotlight or Kramer (outrageously expensive, but places like Target are knocking off things from spendier stores like C&B and Pottery Barn) would suit better, IMO. If you sew or can have pillows sewn, this contemporary tapestry fabric would work wonderfully with your colors. But, you didn't ask that so feel free to tell me to stuff it if you're in love with your pillows. :-) (Pun not intended.)

Your other option is to call the manufacturer of your loveseat to find out if they still make that model and fabric, and go matching. There really is nothing wrong with that.

Johnmari: Thank you for the suggestions and advice. I like the styles of the sofas you mentioned. I considered looking for the matching sofa to the loveseat but then I thought it would be too match-matchy and that the room was plain enough that something different would be an improvement.

It didn't occur to me that I could use pillows to tie together two solid color sofas. I think I like that idea better than searching for a sofa with a printed fabric I like. I also agree with you on the pillow covers, btw -- and have wanted to replace them for some time but since I wasn't sure what the new sofa would look like, I've held off on pillow replacement.

SusieQ07: The picture you attached isn't displaying for me and when I click on it I get a message that the picture no longer exists.

try_hard

Actually, I think the matching route would look just fine. You'd have matching bookcases, ottomans, and couch/loveseat, but your end tables and lamps don't match, you could add plenty of jazzy mismatched but complementary patterned pillows, and definitely put up some more artwork flanking the window. Something big/tall and b@llsy, don't wuss out :-) because you have very high ceilings and a big window. Those varied elements break up the "Rooms to Go" vibe you can get when absolutely everything matches exactly, and you can add all these things without the room looking overfussy and cluttered. If you decided you wanted to put something up on the window, a bamboo or woven-woods Roman shade would look wonderful.

Oh, and if you get pillow covers where the fillers are purchased separately, get fillers that are the next size bigger than the actual cover (like a 20" filler for an 18" cover). It gives a plumper, firmer look that doesn't sag, get floppy, or develop those odd-looking "ears". It can be hard to get them into the cover, a good trick is to leave the thin plastic wrapping on the filler (if the wrapping is thick plastic, take it out of the package and wrap it in a bit of dry-cleaning bag or similar weight plastic), shove it into the cover, then reach in and carefully rip the plastic so you can pull it out.