Going to afternoon tea at Fortnum & Mason. I have no idea what to wear. I was thinking the trusted skinny jeans (dark), heels & blazer with nice top & jewelry but someone told me that I should have a 'tea dress' and keep tops of my arms covered! Now I'm in a bit of a muddle and have no idea what to wear. I don't own a tea dress! I'm 40, slim and petite. Please advise!