It's all about the setting--the mood is created with an ambience and lighting can make or break the setting. My romantic self loves a nice warm candle-lit setting.
Smells are also super important to the mood/ambience. I opt for natural/non-toxic scents because anything else gives me a massive headache. These are a few of my favorite scents that are clean/non-toxic as well.
The furniture & functionality matters. Making a space cozy/comfortable is super important but this will vary highly based on your preferences so find decor & enhancers that work for you. Here are some of mine.