If you and your partner are not wanting to use condoms (which I only recommend if you and your partner are 100% STD & STI free), then I would suggest a form of hormonal birth control. There are plenty of options: the pill, the patch, NuvaRing, even the shot or implant. When used properly, these methods are extremely effective; more than 99% effective against preventing pregnancy.
This sounds pretty good to the 27% or more chance of becoming pregnant while using withdrawal (stats according to Planned Parenthood website).
To be honest, it is actually unknown whether pre-cum contains sperm. There is a much greater chance of pre-cum containing sperm if the man has ejaculated at an early time prior to having sex again, but some studies have shown that most pre-cum actually does NOT contain sperm. Of course, one can never REALLY know. Everything differs from person to person, and whether you want to risk it or not is your personal choice.
I would suggest trying out the pill; if you can remember to take it every day, you are very very well protected against pregnancy. Please consider hormonal protection, or at least condoms.
Best of luck