I cook for two (mostly), and find that the 4 quart is the one used most often. The 3 quart is a bit too small for most meals. My daughter cooks for two, and uses a 6 quart, as she plans to have leftovers for another meal or two. She works from home, and has the flexibility to start a meal during the day.
If I was still working full time, I would look at one of the modern pressure cookers, such as the Instant Pot. They are sometimes referred to as fast slow cookers, and I've seen a lot of recipes for dinners that can be cooked in an hour or less. I keep thinking about getting one, but my wife tells me that I don't need any more cooking equipment. Needs and wants are two different things, though.
You might want to consider how long you are away. Coming home to a warm meal sounds appealing, but most meals would be overcooked if you are away for 10 hours. Browse some of the recipes and see what will work for you.