I have very straight, limp, lifeless hair, which I keep short in a bob. I would like to grow it longer and would like to get a 'demi wave' (if they're still called that) but I also want to keep colouring my hair (I do that every 2-3 months).
If your hair is in healthy condition, you keep it cut regularly, and condition it regularly, you will be able to do both. Keep in mind that every time you color or perm your hair, you're having strong chemicals applied to your hair, and they will be opening up the hair shaft every time.
Any chemical treatment will have an effect on your hair's health. Perming is not recommended until hair is back to health, as perming damaged hair can cause it to break. A demi wave perm (also known as a body wave) is still a chemical treatment, but the chemical solutions are a lot less harsh and damaging to hair than they used to be. If your hair is not too badly damaged, then get demi wave perm.
Most hairstylists would recommend getting the perm first, before coloring the hair to ensure that the perming process does not conflict with the newly applied color. Chemicals in the perm neutralizing solution can react with hair colorants and cause the hair to become lighter. You should wait at least fifteen days after getting a perm to dye your hair.
Short hair can be made wavy hair too.
A body wave perm can last between three and six months depending on how you take care of your hair.
Use a porosity control shampoo before coloring hair so it will absorb the color more evenly.
As long as you said two weeks between the perm and color, you can do both.