Hello all!

My wife and I will be travelling with our son (17 months) from LHR to ORD. He is a lap infant, so we do not need a seat for him. That being said, my wife will be 6 months pregnant on the outbound and 7 months on the return, so I would like her to be comfortable (at least to the extent possible). I have one world sapphire, so can get the MCE for free on an economy ticket. I am between getting 3 of these seats for us, or 2 premium economy. Has anyone been in a similar situation? Happy to hear advice!
Thanks,
J