These exercises are good for people not used to working out or don't have a lot of mobility.
First take your pillow (yeah I said you could stay in the bed I didn't say you were going to be comfortable) and place it on your lower back. It will give lift to help you get more impact on this stomach exercise. Place your hands beside you with your palms on your bed. Lift your feet together (ankles touching) and slowly lift your legs. Keep your stomach muscles tight and take a deep breath in. Continuing to breathe (most people forget to keep breathing), slowly bring your legs apart. Slowly count to 5. Slowly bring your legs together, and then slowly bring them down. Begin 5 and every day after that add one to each time you do the exercise.
Take the pillow out from under you and lay flat on your bed. The twisting in this exercise is great for getting rid of love handles. Place your arms straight out about shoulder length. Roll your head to the right but keep your shoulders and arms flat on the bed. Also while doing that bring your right knee to your chest. Take a deep breath in as your tighten up your stomach muscles. Breathe out as you roll your right knee and to the floor on your left side. You should feel a twist. Do not put too much so don't stretch until it hurts. If you can't reach the floor just go as far as you can. Let your breath out as your roll back slowly into your original position returning your knee and leg too. Take 5 deep breaths and repeat the process starting with twisting your head to the left. Do this exercise on both sides 5 times and increase as when it starts to become easier.
Take two pillows and stack them at the end of your bed. Laying flat on the bed with your feet elevated by the pillows. Over your chest cross your arms. Take a deep breathe in as you pull your stomach in towards your back. Slowly release your breathe as you lift your upper body towards your feet. It does not matter how far you come up toward your feet just as long as it burns. While you are laying back down again don't forget to breathe in. Take a deep breathe and the repeat. Do this exercise 5 times and increase each day.
Lie on your stomach with palms flat on the bed and next to your shoulders. Straighten your arms fully to lift your torso up. Hold for 30 seconds before going back to the starting position. This exercise is quite similar to push-ups. Do this exercise 10 times.
I hope this helps you begin to workout. You have to start somewhere exercising, why not your bed? Remember just because you are in bed does not mean you don't need to stay hydrated.