Romantic places in bangkok?

I am going to Bangkok with my mother-in-law and husband for 6 days. We are going for medical checkup for MIL. I’m hoping we will get some alone time in the evening. Our marriage has been kind of rocky lately and I’m hoping to spend some romantic time outside the apartment with my husband. We will be staying near Bumrungrad area. Can anyone please suggest some romantic places in Bangkok? It doesn’t have to be very cheap. And I’m hoping to get a little unusual answers,,, unusual romantic places... like tree top dinning...