Like you pigeon, I've always had a compulsion to pack much more than I need and to pack things that take up too much space. What I found helpful was to place two empty laundry baskets on the floor. One for clothes and the other one for shoes, purses, umbrellas, hats etc. I begin by placing all the 'must take' items on my bed and tossing the 'maybe don't really need' items into the laundry baskets. If there's still room I'll pull a few items from the L. basket, and if suitcase is too full, I put things back until suitcase can close. I place things like jewelry, scarf, makeup, toothbrush, brush/comb, a sweater and a kindle in a large carry on bag.
Space savers: Take advantage of double duty items such as a beach cover up that can double up as a nightie. Sandals, boots that dress down or up. I travel with a small 'crossbody' purse with passport, personal ID, boarding pass etc. that fits inside the carry on. When I'm not travelling I'm always on the lookout for small (travel size) samples of toothpaste, shampoo, lotion etc. A lightweight, packable jacket is perfect for cold climates and takes up about as much room as a sweater.