Hi Debinmi, for me the best core exercises are Pilates focused. All the exercises you mention are found in Pilates. Others are the Pilates hundred, scissor kick, single leg stretch, double leg stretch, leg circles, russian twist, pendulum (aka windscreen wiper), and reverse crunches. There are also exercises you can do incorporating the foam roller to add an extra core challenge. One I like to do is the dead bug where you lie on the foam roller so it is vertically along your spine and start by raising one leg off at a time then try to raise one leg and the opposite arm at the same time. The longer foam roller is best for this but you can use a shorter one and use a yoga block to support your head. The stability ball is also a good prop for core exercises.
