Mindfulness/meditation are two fold, there is the formal practice where you set aside time to be mindful and then there is the informal, where you incorporate the practice into your everyday activities.
One of the first things I teach my clients in formal practice is to get rid of the notion that you need to sit on the floor to meditate. As long as you are sitting upright and are comfortable, that is all that is important. There are some ideal positions, but if you aren't comfortable you are going to find it very hard to focus. Even if you have to lie down in a bubble bath to practice, but you still practice, its all good with me.