Floss will always fit between the teeth no matter how tight you think they are. ALL teeth, even healthy teeth have some degree of movement, it is this degree of movement that allows the floss between them. Flossing is absolutely needed to prevent gum disease. Gum disease not only leads to tooth loss it also harbors pockets of bacteria below the gum line that can directly deteriorate your general health and quality of life. Flossing is the BEST thing you can do for your health for the least amount of time or effort. It can also save you tens of thousands of dollars in dental work later in life that won't even come close to restoring what you already have right now.
I know what I'm talking about as I once fought the war on tooth decay in the US Air Force during the 70's and I've seen it all, the good, the bad and the ugly