For the last ten years it's been a latte brown/grey, okay greige, 3 seater. I'm loathed to get rid of it as it still is so comfy, though somewhat worn and faded. Desperately trying to the find a drill, cotton or linen in a bright teal/ kingfisher/ peacock blue to re-cover. Something like this...

I can understand the frustration at the thought of obscuring the sliding doors. To avoid that you might consider a pair of sofas that face each other. (Like in the picture attached) This position looks very welcoming as it invites the seated people to face each other for conversation. It does mean for viewing the tv on the 'blank wall' you won't be in the most comfortable position, so I suspect you'll need to compromise somewhere... Access to the door against tv viewing.

I have used Saatchi Art (saatchiart.com) to both browse and purchase art for our home. Original art work can be purchased and most artists have prints at a more affordable price. It's a good place to determine what styles and mediums you love as you can filter your search. For Australian art I love Blue Thumb (bluethumb.com.au). All Aussie and all original. Very few options for cost effective prints unfortunately. I'd be cautious about filling the space for an instant look. As everyone before me has said "art is personal" and as such, I think it should grow with you and your space. Start with one piece that you really love, big or small and work around that. I have found that putting unusual unexpected items on the wall makes for interesting 'art'. My husband's baby shoes (circa 1953) and now our children's first shoes are objects that always create conversation when guests come over. I have a Mexican art cross (we're not religious, the colours and the metal work drew me to it), a vintage wooden Indian spindle, African birds in a tree hand-beaten and cut from a steel drum, a clay mask my daughter made in art class, a woven Maori kit bag, some art that our kids have done at school (put into Ikea frames so they are always the right size. We change them as something else we love comes home), a hand-made ceramic tile, a growing collection of geckos found in antique stores, vintage travel posters in frames, (I'll stop listing what we have!)...all these items and more, have been collected over the last 20 years and put up around our collection of art or in clusters to create stories. I've collected the initials of our family (yes the child with the "K" is not thrilled it's so small and the child with the "G" feels he's by far the favourite! Needless to say both will be replaced in the future when a more appropriate size comes to light) from vintage stores both here and overseas. Our walls are a growing collection of art and objects and at any time I can move things around and change the composition as a new item is discovered. Best advice I can give you is to have fun with it, enjoy creating your own gallery, it's for you to love you're not required to impress anyone else.

How many people do you want to seat? Is that a walk through beside the stairs? Is there a view out the window? My first instinct is to say two sofas facing each other so everyone can see out the window and enjoy conversation.