From someone who sleeps 8 hours almost every night: just go to sleep earlier and /or wake up later.
Impossible to give any better advice without any further information. Is the problem not enough hours in the day (e.g. time wasted on stuff like commuting etc.)? Or are you just unable to stay asleep longer than 6 hours?
Reading works for me. Recently I've improved that even more using an eReader.
My room is completely dark when I go to sleep. I use blackout curtains and have removed any sources of light from my room. In the summer it gets light very early in the UK (~04:00) and I require ventilation so I also wear an eye mask. I use a fan to mask any background noise and, in summer, this is blowing directly on me to keep me cool. I use a wool duvet which I found the best for temperature regulation; I require a weighty covering even when it's warm.
I use a Kobo which has an adjustable frontlight that can go both very low and very warm (redish). I set the Kobo's backlight to the lowest and warmest possible setting. I lie on my side with the Kobo on its side leaning on an adjacent pillow such that I don't have to hold it. Turning pages requires a light tap; there is no scrolling or swiping involved. At some point after a few pages of Iain M. Banks, or whatever I'm reading at the time (usually science fiction), I fall asleep. The Kobo automatically switches itself off after I stop turning pages and I wake in the morning with it next to me (or sometimes I've moved it but can't remember when/why).
It's important not to use something like TV that you need to actively switch off at some point and, if you use an object like a book or eReader, make sure it won't fall and wake you up when you start to nod off. Definitely don't hold it up with your hands. Don't use a phone because scrolling etc. is far too active and backlit screens just don't seem conducive to sleep. An eReader is perfect because it means you can turn the lights off but the frontlit e-ink screen is more like a book than a phone.
This method has been tried and tested with a partner in the same bed. You just need to make sure any objects don't fall on or get tangled up with said partner. I have a pillow system propped up by my bedside table for this purpose.
Impossible to give any better advice without any further information. Is the problem not enough hours in the day (e.g. time wasted on stuff like commuting etc.)? Or are you just unable to stay asleep longer than 6 hours?