I know there's a floor insulation issue, but what about redirecting air, and other sources of leaks? Does your basement have vents in it? Turn them off and maybe consider getting bent covers that can seal in the summer. Close the vents on the first floor so that (the majority of) the cool air comes in at the second floor and sinks down. Weather-strip and baffle the basement door.
Also, see if your electric company offers a home energy assessment. It takes about an hour, and there are usually two tiers: free, and a second tier where you pay for a blow test. They can make some recommendations on making your home more energy efficient.
I had a friend who made a point of "needing" to go into the office an average of one day every week during the pandemic. His logic was that, if his job could be done entirely from the comfort of his living room in the suburbs, eventually the bosses would realize that it could also be done entirely from the comfort of someone else's living room in the Philippines or India.
I'd suggest refining some of your ideas. Are you looking for traditional trees and bushes, or do you want color? If you want color, which colors? Do you want something blooming every season? Do you want low maintenance? How drought tolerant should it be?
Are you looking for ornamental plants? Do you want fruiting trees or bushes? Do you want to grow your own herbs and maybe some veggies? Do you want something pollinator friendly? Etc etc.