Child Custody Arrangement Following Separation

My partner and I have separated after five years together. We have two children aged 7 and 4, and we're trying to work out a fair arrangement for custody and contact. We're both keen to keep things amicable for the children's sake, but we need proper legal guidance to make sure everything is documented correctly and protects everyone involved. We haven't been married, so I'm also unclear about parental rights. We've tried discussing it ourselves but realised we need professional advice before making any agreements. We'd like help understanding our legal positions and drafting a formal arrangement that a court would recognise if needed in future. What I'm looking for: Legal advice on parental rights, custody options, and help creating a formalised child arrangement agreement.