I think it is hard to do it by percentages -- it seems rather abstract and unresponsive to individual situations. If you are building a wardrobe from scratch you might need to spend more in a given year (if possible, of course). If you are merely maintaining, you could manage with less. I also think 5% for a family of 4 is a bit unrealistic. As Laura said, kids' clothes may be cheaper but they grow out of them quickly (and even if you get mostly second hand for kids' clothes, shoes and boots are pricey).
Having said that, I spend roughly 5% of my income on my clothes. Less some years, and more in the years when I was building my closet. One year it was closer to 10% I think. I had no foundations (literally) and it cost a lot to set up the basis.
I'd find the needs/ wants/ savings system difficult to use also because is clothing a "need" or a "want?" Some of us are probably prone to describe almost everything as a "want" (TG, sounds like you fall into that camp); others probably consider almost everything a "need." With some items (puffer coat) there really isn't any option -- but you can still cheap out by telling yourself you don't need a super-warm or nice one; an "okay" one will fill the need. And, contrariwise, how easy it seems for some of us to decide we absolutely need those high heel shoes (that we won't wear more than twice in five years...).
I guess this is a long-winded way of saying that I have not set a per month budget but I do keep an eye on what I spend each season and aim for a seasonal budget of sorts, which I leave a bit flexible. That's because my income isn't fixed but variable and I might have more or less room to play with clothes.