Even when we are persuaded by beauty journalists and bloggers that we ‘need’ a serum, it often gets used infrequently as an add- on to our skincare routine and sometimes just languishes at the back of the cupboard. But if you use a serum you don't need to use a cream as well. You are really just doubling up. 

Serums contain all of the good ingredients that may or may not be in your cream moisturisers and none of the fillers and unnecessary ingredients.  This is why some people add a few drops of serum to their moisturiser. I am not saying that creams are bad, just that serums can certainly be a valid replacement and not just an add on. 

I like to apply my serum to clean, damp skin.  Damp is not essential but it feels gorgeous.  I then apply a little foundation which goes on beautifully over serum.  If you use just serum for a week or so, I can guarantee you will not feel the need to go back to cream.  A change is as good as a rest. 
Give it a go :)