One of my favourite wardrobe stables is long t-shirts. They are a stable piece because you can wear them in many ways and combine them with almost everything. I got two long tees in my wardrobe. A black one and a white one, both from Zara.
Long t-shirts are everything. I wear them underneath a sweater, knit or cardigan, but you can also wear them as a dress. You can also tug them under your bra and make them a little cropped. Last but not least, you can wear this tee with a waistbelt or put it in a knot at the bottom. What I love most about these tees is that you can be creative with them and wear them whoever you like.
You can find some links to similar pieces down below.