I think mindfulness and heedfulness are almost interchangeable. Mindfulness is a better word to use in the context of meditation, and heedfulness is a better word to use in the context of living a good life (making merit by practicing sila, dana, and bhavana).
I think being heedful means avoiding bad actions and doing good actions. For example, if someone insults you, but you remember to stay calm because you know that getting angry is bad kamma, then you are being heedful. If you remember to avoid idle chatter or pointless talks in conversations, you are being heedful and speaking mindfully. If you remember to practice dana whenever you can, you are also being heedful.
I think being mindful doesn’t necessarily mean you are noting your actions. You don’t necessarily have to mentally say “Walking… Sitting… Standing”.
You can be mindful when you walk, sit, stand, or talk without noting.
For example, let’s say you practice breath meditation and you are aware of the breath all the time. Because you are mindful of the breath and not day dreaming, you are naturally aware of what you are doing in the moment whether that be sitting, standing, or walking. In other words, if you are staying in the present moment and devoted to your meditation object, you are being mindful.