Huge hugs, I hope the last couple of days have been better. I'm sure it is all phases and will be better next year when you are back in school. Both baby & toddler will be older and out of this phase. I remember feeling broken with exhaustion this time last year. Our days are still tiring butvour nights are much improved now.
Not sure what to suggest for your DS. I understand the mattress on the floor option. I do it for illness but on a regular basis it might become something he depends on.
Is it possible that the NWs are from becoming OT since dropping the nap? I understand he no longer would take it, which is fine, but would he benefit from an earlier bedtime? It sounds unlikely but often LOs sleep gets worse as they get more & more tired & giving opportunity for more sleep can actually work and lead to better sleep.