The form to work with is the D81 statement of information. It's on the link here: https://www.gov.uk/government/publications/form-d81-statement-of-information-for-a-consent-order-in-relation-to-a-financial-remedy
This is what you would submit to the court alongside the consent order that you will have drafted up.
In most cases the consent order will set out what is known as a clean break - ending the financial ties between you. The issue of child maintenance is separate from this so that would still continue even after a clean break agreement.
If you have the D81 fully completed, a lawyer can work from that to draft the consent order for you. It does need writing up by a lawyer, normally, the language that is needed and the compulsory terms required aren't readily accessible to the general public.
But, for example, in my private practice this would only be a couple of hours' work and so the cost should be reasonable, no matter who you go to for this to be drafted.
You both need to make sure you have had advice on the terms agreed in the order.
You then submit this to court, along with the Form A, here: https://www.gov.uk/government/publications/form-a-notice-of-intention-to-proceed-with-an-application-for-a-financial-order
The fee to apply is £255.
I hope that this answers your question?
Thank you for your enquiry today. I am happy to answer follow-up questions - please do get in touch with requests for extra information or further queries and I will do my best to help you.