I typically sit on my bed actually. It's a comfortable space for me and it helps me let go. I try to sit up straight, I'd like to foster better posture but sometimes I let it go if I'm thinking too much about It.
I will do my mediation sitting in the floor. I am comfortable sitting and get morning sunlight. Also watch the plants around.
I alternate; some mornings I do my meditation on a pillow on the floor with my legs crossed, other days I do it sitting up in the chair where I drink my morning coffee. I think whatever works best for you is good, so long as your spine is relatively straight.
I prefer to always meditate sitting up on the floor. To feel more comfortable, I place a flatter pillow underneath me and it helps prop me up.
I mostly do on the chair , not a sofa but a chair with a straight back.. helps with the upright position and the chair shouldn't be too tall, the soles of your bare feet should feel the ground…it helps more with the sensation