covert masturbation

Hi all, although we have an active sex life I am finding I am often horny within a day or two of sex. However my wife is not. So to combat this I often take myself off to masturbate to eleviate the tension without my wife knowing. I am not able to get the me time in order to satisfy myself properly so feel like I have used myself and a bit guilty that i have done so behind my wife's back.
What I am planning is to tell my wife when I am horny, so she can decide if she wants to have sex or let me 'sort myself out'
if it is the later I'll ask her if she wamts to watch or even help. That way I should hopefully be able to feel fullfilled between sex by having eniugh time to satisfy myself openly.
Is it the norm to masturbate without your partner knowing?
does my plan sound fair?