I looked back at where you said we have room for one more little flowering shrub for attracting hummingbirds. Actually some of the best hummingbird attractors are vines. It is easy to have space for a little trellis somewhere. If you want something that will stay small, cardinal climber and the related cypress vines are annuals that need to be started over from seed each year. They are very dainty and delicate and only grow about 8-10 feet tall, so they don't need anything sturdy as trellis. I have one on a little trellis that's just a couple feet tall and I just keep weaving it all around and through the trellis. They get covered in little red trumpet shaped flowers that hummingbirds love.
If you don't want to start over every year and can provide sturdier trellis, you can plant trumpet honeysuckle (lonicera semperviren) or trumpet creeper. The trumpet honeysuckle is more manageable. The trumpet creeper spends the first few years getting established, doing nothing much, not even blooming, and then it takes off and gets gigantic. Do NOT plant it next to your house unless you want to spend the rest of your life pulling it off your roof and out of your gutters. But if you have a space for it somewhere away from the house, it is a very nice habitat plant. After it blooms, it makes long slender seed pods, which are very hard and impossible to open. They stay on the plant for months and only open after there have been some hard freezes. Then they open to reveal hundreds of paper thin seeds which finches and other birds like. In mid winter when there is very little other food around, birds congregate on the trumpet creeper vine (which stays conveniently up above the snow) for those seeds.