I don't think you have to buy anything fancy with attached rails - if you can put the bed against a wall, then you can just buy one of those folding bed rails for the open side. Resale shops like Children's Orchard often have them.
You could consider skipping the toddler bed entirely and go to a twin if you have the above rail. However, since you have another one on the way, you'll get double usage out of a toddler bed.
You could take your daughter to buy something special for her new bed - new sheets or some throw pillows in fun shapes or cartoon characters. Those also help take up some of the extra space in the new huge bed so she doesn't feel like she's swimming in it - those twin beds look awfully big after a crib! Those big bolster pillows are really popular in college dorms so you can often find them in places like Target and Sears - you can put one against the wall side and help her feel snug, but they'll also last a long while and can be used for other purposes.
ON the chair issue, friends of mine bought each of their kids a high chair at Mill Stores - unfinished - and painted it themselves. It has arms and a footrest, but no tray. It's wood like the other grown-up chairs so the kids like it - it doesn't feel kiddie style. The child could even pick the color or put some decals on it (maybe letters with her name, or her favorite animal or character - however much you want to engage her in those choices. If it's her special big-girl chair, she might sit in it. You can push it right up to the table so she really can't stand up in it - her legs are under the table, just like yours, and there really isn't too much room to wiggle around. If some restraint is still necessary, you could use some kind of a belt and secure it at the back of the chair where she can't reach the buckle and fiddle with it! My friends' daughter is 2 and she just loves her chair, so they don't even need a belt of any kind.
Good luck!