The 35-year-old singer has been dating the `Firework` hitmaker for around six months and sources say he`s so smitten with "independent" Katy, he is considering popping the question.
A friend said: "John really likes the fact that Katy is so independent and not needy and clingy like the other girls he`s dated. This is the first time John`s felt so strongly about a girl. She`s played her cards perfectly.
"They really do bring out the best in each other. It wouldn`t surprise me at all if he proposed."
Sources also say 28-year-old Katy - whose divorce from Russell Brand was finalised last July - is keen to settle down and is even thinking about having children with John.
One revealed to more! magazine: "John has given her the confidence to jump out of the rat race. With John, she feels like herself. She wants to nest. She`s gained a few pounds, is taking a much-needed break from work and perhaps is even getting her mind and body ready for pregnancy."