joeweekend's advice is spot on. Silicone-based lube is clearly the way to go. There's a brand called "wet" that normally produces water-based lube, but they have a perfectly good silicone lube that sells for a bit less than others. I'm not sure if it sells in your neck of the woods, though. Regardless, you definitely, definitely, definitely want silicone based lube. It's as slippery as an oil-based lube but it won't wreck your condom.
Also, after you've got a bit of your dick in, pull it out and reapply. Repeatedly. You're basically using your dick to apply lube to the inside of your partner, so the more lube you can get in there the better. You can make it fun, turn it in to foreplay. It doesn't hurt to tell your partner how hot it is that he's taking your cock, and how horny and happy it makes you. There's no lubricant out there like feeling as though you're doing a good job, and the last thing you want is for your partner to feel like it's hard, tedious work mounting your cock.
And don't forget to enjoy trying. Even if it doesn't work you're still fucking, and fucking should be enjoyable, no? :)