I use one of these: http://imgur.com/8A3dopG

For some teeth, I have to force it a little, my teeth are pretty close too. Its so worth it though: much better breath, clean feel, minimized risk of cavities.

I avoided purchasing one by forming a loop with the wire. I cut a 20cm (8in) piece, then I tie a triple knot (the simple over hand knot with both ends). The wire is very slippery so I move the first knot as close to the ends as possible, so as not to waste floss.

Having a loop allows to have a firm hold on the floss and adjust tension. I use it with both hands though. And I waste very little floss because I can rotate the loop and use every inch of it.

I've tried them, but they refuse to go in too.

I use these. I can bit down on it if I need extra force. http://www.apteekkituotteet.fi/WebRoot/Euran/Shops/Eura/506D...

Of course people's teeth are different. I know some prefer these, where you push it in from the side. http://www.tepe.com/uk/products/interdental-brushes/

Thing is, teeth are so close to each other that literally nothing can get between them, not even food. I have however few teeth that get food in between, but these are the ones that already went bad and were fixed, and have gaps as a result of that.