Have you gotten to the bit yet where Aldort talks about when verbally validating hurts? She points out that you can silently validate a child, just be present for them. You don't necessarily have to provide verbal validation or physical contact. I found that to be very reassuring, because my mid-tantrum 3 y/o will scream at me "NO!! I'm NOT angry!!!" (or frustrated, or sad, or scared, or whatever).
You didn't ask for suggestions about the floor scenario but I thought I'd offer one anyway...do you have a splash mat? My boys often like to "picnic" in the living room and I don't like the mess that usually comes with it, but we can compromise by putting a mat down on the floor, and they eat on that. (Our splash mat is a coated cloth from Mimi the Sardine)
may my heart always be open to little birds who are the secrets of living whatever they sing is better than to know - e.e. cummings