The answer to that is, "get out of the metro". Cities are designed for singles and DINKs. There's a reason people talk about moving to the country, building a little house, starting a garden, etc... it's a better life for a family, and sustainable.
Living in the country is in no way more sustainable. It's far less sustainable for the environment as people must drive everywhere. Infrastructure for water, sewer, trash, etc. all cost more (regardless of whether the homeowner pays the increased cost) and cause more environmental impact as they're less efficient due to lower density.
You might find it to be a better life (I don't) but it's not more sustainable.
Small town with car: go a few blocks, never stopping for traffic, going the direction you like and stopping where you please
Big city with car: go many blocks, constantly stopping in traffic, route around 1-way streets, and then slowly loop around looking for a place to park
Big city with bus: go many blocks, constantly stopping in traffic, route around 1-way streets, often going kind of the wrong direction, spewing diesel soot all the way -- and often the bus runs nearly empty, a big soot-spewing vehicle with almost no people
Big city driving is often not driving at all. Want to grab some milk? Walk to the store. Want to go to a restaurant? Walk.
That's obviously not all city transit but it's a much larger part. Also lots of grocery stores still have parking lots (actually garages) in the city. If you're going somewhere like that you can still park easily. Depends on the location I'm sure.
I'm not sure what your dislike of buses is. They are far more efficient than personal transit from a fuel perspective. A bus can be "nearly empty" and still replace a half dozen cars. And at peak times a bus will replace dozens. There are issues with buses but "soot-spewing" isn't one of them, at least not relative to cars.
Small town is also not really country. If you can drive a few blocks to the grocery store, you don't live in the country. In fact, if your house is near blocks, you don't live in the country. Small towns are of course also less sustainable than cities as small towns are basically built like suburbs.
You're assuming city life and country life are largely the same. In the country you don't pop down to the market 3-4 times a week when you run out of milk or want to grab a sandwich -- you buy a deep freeze and go "big shopping" once every week or two.
I lived in the country for years. Yes, you buy a deep freeze. You also drive 20 minutes to the grocery store and 20 minutes to drop off your kids and 45 minutes to work. Yes, you optimize for bigger grocery trips, but the fact is that you still drive everywhere and you drive further because nothing is close.
Nah, you just plan better and around a life that doesn't involve a ton of time in the car. Drop off the kids and then shop right after, or hit the store on the way home from work, or let the kids take the bus. Fewer extracurriculars for them but I assume since it's the country there's plenty of other stuff to do.
What IS nice is that the car time tends to be long like you said, 20 minutes, 40 minutes, which is more efficient energy-wise and for wear and tear than a bunch of little 5 minute trips.
You have to live a place that's right for you. I'm perfectly fine not leaving the house for days on end, there's plenty to do around here. Some of my friends would go crazy if they didn't have someplace to go every night. If you're the latter kind of person, country living is probably not going to agree with you! The same is true vice versa -- how do I go to Costco on my bike!? ;)
Unfortunately, it also results in a lack of structured activities, social groups, etc etc. Unless you're willing to spend half your life driving, of course.
