I want to get more serious with meditation, but it is never comfortable for me.

So I have a few questions about meditation. This year, I have decided to get real serious about meditation, and connect with a deeper part of myself that I believe has been dormant for a while. I have been meditating every night before sleep for about 10 minutes, but sometimes I miss it and don't meditate. I have never really researched too deeply on all the different meditation practices, so I just sit down and focus my attention on sounds, my body, and my breath.

However, my back is never comfortable. I feel that the curvature of my spine is not natural, and I slouch very often. This becomes VERY annoying when I'm meditating, which takes me away from the experience. I sometimes feel my body have some very strong urges to just move and correct my spine, but all that I want to do is sit down and not move, just observe. Sometimes these urges almost try to force me to open my eyes and stop meditating, as if it's a voice screaming at me saying "just stop doing this for the love of god! Open your eyes and move around". How can I improve this? Also, I don't know if this is relevant or not, but I have been diagnosed with ADHD at an early age, so maybe that might play a role in it, even though I don't believe that this condition stops me from meditating at all.

On a second note, I want to increase my meditation time since I feel that 10 minutes is not enough anymore, I want deeper meditations. Is there any kind of meditation that I could start doing with that in mind? I'm thinking of starting with maybe 30 minutes, and then move to 1 hour, and perhaps even longer than that if I can.