I believe I have settled on a planet for my human-like aliens to come from - Tau Ceti f. This choice brings up a whole new set of questions based on this information:
Assuming that Tau Ceti f is a terrestrial planet, it would likely be at least 2.3 times larger in size than the Earth. Assuming an Earth-like atmosphere, the surface temperature would be approximately −40°C (233 K). With a denser atmosphere able to produce a stronger greenhouse effect it could have a much higher temperature, between 0 °C and 50 °C, enough for complex life to exist.
Let's say I wanted the planet to have this "denser" atmosphere so my characters wouldn't be living in below zero temperatures. How much denser would it have to be? What would the sky look like? What effect would it have on people who lived there? What would the weather be like? If a person from Earth came to this planet, what effect would it have on them? If a person was used to living in this denser atmosphere and they went to Earth, what effect would the change have on them? What would it feel like?
I Googled "living in a denser atmosphere" and got a variety of answers. One site said living creatures would feel no effects even in a very dense atmosphere because we would evolve to adapt, another said everything would grow bigger, another said there would be no land just water... the only thing they all agreed on was that people would be able to strap on wings and fly in a denser atmosphere. I really don't know what other search terms will yield me answers to my questions.