Here's our most basic model...just a simple basket we found at Target that seemed sturdy, comfy and we use a pillow in the back. You can choose a basket based on the size you need. Obviously this one's not gonna work anymore for those long legs...not really a true corner chair but a similar concept. If you could find a taller one, that would be more like it. A rubbermaid tub in the right size would work, or laundry basket, but obviously not as aesthetically pleasing as an actual lined basket if you're going to use it in your family room.
For the abductor, my mom just had a block cut from foam at Joann's, and made a cute matching cover for it. She sewed Velcro onto the abductor cover which we secured to the mat using self adhesive velcro from Joanns. You could probably just cover the foam block in something sticky (colored duct tape, contact type paper, etc., and not even have to sew the Velcro to the block, if it would stick, but we haven't tested it.) Yes, mom is available for custom sewing projects - she does a great job, just comment me if you are interested in having something done. :)
Finally, we do a corner chair in his crib using kitchen chair cushions.
While we're on the subject of things we've found useful here are a couple others you might like
1) tummy time mat- if your little one has trouble on his tummy like Mason does (mostly a sensory issue with his face, and super painful shoulders)...here's an easy sensory friendly mat you can make too...(just cut a piece of egg crate to size and zip it inside a supersoft body pillowcase ($10). You can add an extra piece near the top to give it some elevation/contour. We stretch his shoulders using arm splints to keep him from bending them up too close to stretch. This mat gives him a comfy hip stretch too. He doesn't enjoy it at all lol ;)
2 ) Sensory play area - we used the top bunk off Micah's bunk bed set for Mason's discovery area. It works well since it has guard rails built in already almost the entire length around. We put a lot of high contrast toys in it and make sure there's plenty of place for rolling (he doesn't roll off his back on his own yet, but this motivates him to try). We use an old crib bumper around it, especially around the opening, so he doesn't bump his head or fall out. It's supposed to be a "safe" area where he knows he can go wherever he wants.
3) Oxo tot sprout chair - we didn't make this chair obviously, but we looked a long time for something to suit Mason's needs that wasn't another giant piece of equipment. It has a 5 point harness, high back, great tray for suction toys, sturdy abductor and adjustable footrest, plus fit well into our living room. It is good for kids up to 60 pounds (36 months to 60 lbs is really meant to be used without the abductor and tray but I think it would still work...most kids that size just don't need it).