Yes of course mantra meditation is more of a mental and energetic type of meditation but there are still ways to prepare the body to make mantra meditation that much easier and more effective for you.
If you do practice a mind body discipline such as yoga or tai chi, it can be a good idea to do this before moving into the more still types of meditations. It warms up both the body and the mind to be placed in a better position to start a meditation practice. This would be the best practice scenario. It is not by any means mandatory.
Assist the body for concentration by preparing a comfortable sitting position. Use whatever props you need to make the position comfortable for you to stay still, such as cushions, bolsters, rugs or a chair if you need. The aim is to be comfortable without the need for fidgeting with a spine that is in alignment.
The best sitting positions are those that easily hold the spine in alignment. In whatever position you go for, aim for an aligned spine. An aligned spine facilities better energy flow and concentration for meditation.
Cross legged sitting positions are good. So to are all the variations of these such as the lotus and half lotus if you have the flexibility.
Otherwise try the yoga position where shins are parallel to the floor, knees folded and one sits on the flats of their feet. Cushions can be put under feet and buttocks to make it more comfortable.
If you can manage cross legged sitting positions, one of the easiest ways to get spinal alignment with minimal effort is to simply have the posture in such a way so that the hips are tilted forward.
To do this use a cushion and be sitting at the forward edge of the cushion. Position the sitting bones off the edge of the cushion while the rest of the buttocks are on the cushion. Due to the position of the sitting bones, the hips are naturally tilted forward and this forward action puts the spine into natural alignment. Very little effort or energy is needed to maintain this alignment.
If sitting on the floor doesn’t work for you, use a chair. Preferably a hard chair that supports your posture to maintain an aligned spine and not a sofa chair that aids sleeping!
Hands can rest on the knees facing up or down or in the lap facing in an upward cupped position, in chin mudra where the tips of the thumb and forefinger come together or another mudra of your choice.
Be sure to find a comfortable position that you can hold for the duration of your practice and then stick to it. You may experience a little discomfort in the posture if your body is new to sitting positions such as these. However never put the body in major pain. Major pain is not the objective. Always listen to your body’s needs and act accordingly.
With time your body will build up stamina to be able to spend more time in meditation positions and this is part of the discipline. Being able to control the body translates into learning to control the mind as well which is part of the practice.
A good position will help to facilitate a good meditation practice and maximize your results. Eventually your body will find comfort and a home in the meditation position as your mantra meditation practice progresses.