A bulkhead seat is your best bet since upgrading is not an option. Put your carry-on on the floor in front of you and you have a nice foot rest for you to really lay out on.
A lot of people with young babies always try for the bulkhead since they have a spot to let the baby lay and sleep. I've seen where the flight attendant will ask someone in the bulkhead if they wouldn't mind giving up their seat for the baby/guardian. Always refuse to change seats unless it is to a better seat. The only seats better than the bulkhead are upgrades to business/first class.
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