When you find someone who you really do want to be in a relationship with, it will come easier to you to do more romantic things, because you want to. By the sounds of it you just don’t have a current relationship you want to take to the next level. Old fashioned things are the best imo. Opening car doors, carrying bags etc. that’s the stuff that will keep her thinking ab you!
It’s not all that different from a friendship in hindsight. Casual hangouts are more common, with occasional dates thrown in. The biggest difference is the physical aspect, like cuddling holding hands etc. I talk to my boyfriend and best friend about the same things, so conversation wise there’s no differ