I have tried searching for an answer but have got nothing satisfactory. I heard that you are not allowed to pray in your heart/mind and at the very least must move your lips when reciting the Quran during prayer because one of the main aspects of prayer is recitation and that reading from the heart/mind doesn't count. Sometimes praying silently and within the mind (not moving lips or whispering) can feel a lot better and it may be harder to pray if you have to recite woth your lips moving and at least something can be heard. Can't we pray completelt silently and from the heart/mind or does there have to be at least some lip movement or sound to be heard during prayer?
Prayer is all about the conversation between Allah the Almighty and the human being. But in some cases you should recite in some how loud that only you can hear by yourself that not diverge your attention anywhere. As you say if you are reciting in your heart you feel much better and prayer is all about the 'Ajizi' and full attention then you can recite in your heart just whispering in your heart and having full attention and comfort.