I don't want to be right, but I knew I would be 
You could approach it non aggressively. Not even mention the pension if you don't feel ready yet for the fight. I would simply say "it's clear we're over and I honestly don't see the point in this agreement, we might as well just go through the proper divorce process so I'll make an appointment with a solicitor and take it from there"
It can be a good way, to "hide" behind a solicitor. Let them be the reason you insist on a pension CETV, etc.
Never trust anyone to pay maintenance. Actually I expect the majority do pay with no issue. But there are enough arseholes that will dick around, lie, hide income... depends a bit on his job - own company = high risk of paying the OW to hide his salary. Teacher = transparent and attachment of earnings possibly. My advice is to approach the settlement assuming maintenance isn't guaranteed. As you have a child with additional needs, that might mean you should prioritise security of housing.
His pension will be a MAJOR asset. And he knows it.
Remember that he is a cheating liar - so you also can't trust him in the divorce.
Btw, I am not the screw him over type, despite how I may come across
I believe in FAIR.
In my own split, I took 20% of total assets to my solicitor's bemusement. Because I chose to exclude (mentally, it was in the assets declaration) his business - built up before I met him.
He has no legal or moral right to rush you.
It's also an option to press the red button "you are a liar, a cheat and a cunt and you can fuck off if you think I'm stupid enough to sign your pathetic faux legal unfair "agreement" with seeing a solicitor". Then slowly rip it to pieces and let it flutter to his feet as you turn heel and walk head high off to do something more interesting today.