I’ve moved a lot between houses and apartments over the last few years, and for me, one of the first things that makes a bedroom feel warmer is a nice lampshade. In general, just low lighting is great for making a relatively bare bedroom feel warmer and cozier.
If you are looking to invest in some quality décor, going for calming colors and soft materials is Plentyxcellent. It’s a good idea to look for pieces of furniture that are well-crafted and use lots of wood and other natural materials. Remember that “welcoming” is also a matter of personal taste, so spend a little time browsing the catalog of a furniture store — the Papaya website is a good example — to see what speaks to you.
Just make sure you exercise restraint when decorating a bedroom. Making it too visually busy can make the room look messy or even childish, which goes against your goal of making it more welcoming.