Onions are easy to grow, take up very little room in your garden, cohabitate well with other plants (except peas), and come in many shapes, styles and flavors. As long as your soil is well drained, you should have no trouble growing onions. The other great thing about onion plants is you can pick them when you want them - or leave them in the ground for later. No rush.
But we don't sell many onion plants. I think there is something just a little confusing about onions. Seed, plants or sets? Long day or short day? Bulbing or bunching?
Onions are slow. And they can be interrupted. If you want simple green garden onions (bunching, scallion, or 'green'), start seeds inside for transplant or buy little plants for transplant as soon as you can work the soil. You can plant them in a row or in little bunches or in pots - they don't really care. Harvest whenever they reach the size you like.
Most onion seeds and sets are adapted to grow anywhere from Carmel north to Seattle so don't worry about your latitude (30 - 50 degrees). My latitude here in Aromas, California happens to be 36 degrees - the same as Tunis, North Africa. Florence, Italy is a little further north. (You can look up your exact latitude on Google's Latitude Finder.) Regarding onions, latitude is only important because it influences day length and those big bulbing onions need a longer day to develop size. There are specific varieties known as short day onions that will produce a bulb in Austin, Texas.
Since we have a long day and a long growing period, we can start onions in the fall and leave them in the ground over winter. They will rest a bit during the dark days of January and then continue with their work when the weather warms and the days lengthen. Onions sets - those little immature dried bulbing onions - are more for people who have cold winters - though they do well here if you are in a big hurry. You can even grow your own sets by starting a thousand little seeds in a gallon container, let them go until fall, then separate and cut the tops down to 3 inches, trim the roots to about an inch, and store in a cool dry spot until the next spring.
Homegrown onions taste good and are mighty convenient. I had an Uncle Johnny who was what used to be called a 'truck' gardener. He was happiest sitting on a three legged stool in his garden, munching on green onions pulled right from the ground while he watched his nieces and nephews pick peas for the market. Give it a try.