Good to hear that you enjoy your sex life with your wife in spite of what you might consider a short-cumming (sorry, I couldn't resist...). If you know that your wife would be just that little bit happier if you could last longer, then there are many things to try.
I haven't really done the research into those nasal sprays often spruiked on TV with those God-awful ads but they might be your ticket to bliss. Do your research and if the science adds up for you, then you can invest the money into trying it out.
If you're not quite ready to try a medicinal solution, you can simply try sex with condoms just to see if you can desensitise your penis enough to go the distance for your wife. If using a condom actually works against you and you lose your erection, then you might have to employ some Eastern philosophies and read up on Tantra.
If you're not quite up to reading the lengthy teachings of Tantra, you might just need to spend some time on your ownsome and train your brain and penis to resist the urge to orgasm. The next time you masturbate, try putting off orgasm as long as you can. This may involve learning breathing techniques and being able to identify the point of no return, and the point before the point of no return.
Get your wife to help you out where possible. She might enjoy the idea of playing dominatrix and make it her job to stop you from cumming!