No renovation, no drilling, and nothing that needs a landlord's permission.
A flat that looks considered is rarely the expensive one. It is the one where a few decisions were made deliberately and then repeated. Here are five that work in a rented Mediterranean flat, where you cannot repaint, should not drill, and are working with tiled floors and hard light.
1. Cut the palette down

Pick two or three tones and repeat them across the room. Warm sand, soft white, deep navy. When colours echo each other a space reads as intentional rather than accumulated, and repetition costs nothing.
Textiles are the cheapest way to hold a palette together, because you can swap them without touching the flat. The awning stripe cushion covers are made from canvas originally developed for sun protection, 60 percent acrylic and 40 percent polyester, at 24.90 euros.
2. Upgrade the textiles before anything else
Towels, bedding, cushion covers. Textiles are what you touch every day, and the difference between a thin towel and a heavy one is obvious in a way that a more expensive lamp is not.
The Hotel Luxury bath towel is 800 gsm combed cotton with dual stitching, at 23.10 euros. On the bed, the Basic duvet cover in olive green is 100 percent cotton with hidden buttons, from 35.99 euros. Pillowcases and a fitted sheet are not included, which is worth knowing before you order.
3. Leave surfaces empty

Resist filling every shelf. One well-chosen object says more than ten competing for attention, and empty space is the clearest signal that a room was arranged rather than filled.
If you are going to put one thing out, make it something with a story behind it. The Medina bowls are handcrafted in Córdoba, so no two are quite the same, and they start at 12.90 euros.
4. Work with the light you have
Mediterranean light is strong and directional, which is an advantage once you stop blocking it. Swap heavy curtains for lighter fabric, keep the glass clean, and put a mirror opposite the window rather than on the wall beside it.
The Queens rectangular mirror has a slim matte black frame and a reversible design, so it hangs vertically or horizontally depending on the wall, from 106.05 euros. In a rental, get written permission before fixing it, or lean a larger mirror against the wall instead.
5. Buy less, and buy it once
One mug you actually like beats six you tolerate. That is the whole idea. When every object in a room has earned its place the room reads as considered, and considered is usually what people mean when they say expensive.
Scent belongs here too, and it is the cheapest thing on this list to get right. The St. Moritz soy candle has a wood wick that crackles as it burns, opening on vanilla and settling into rose, at 34.70 euros.
Where to start
If you only do one of these, do the textiles. It is the fastest visible change and the one you notice daily. Start with towels and robes, then bedding, then the living range.
Renting? These fittings need no drilling and come with you when the contract ends: No-Drill Bathroom Fittings for Renters in Spain.

