You can certainly ask to use a mediator, who will be independent of both of you and therefore impatial and able to help you both reach an agreement for a consent order if your ex engages with the process. But your ex doesn't have to agree to mediation.
If you cannot get agreement for a consent order with the help of a mediator, one of you will need to apply to court on Form A, and the court will list the matter for a hearing to see if a Judge can help you agree.
If you still cannot agree, the matter will be set down for a new Judge to decide how to split the assets. You will both also need to complete full financial disclosure, so each of you, and ultimately the judge, can see what assets there are and what is available to share. This includes everything from savings, property to pensions etc.
Until you each have full disclosure it is impossible to say what the potential outcome will be, but as stated above, the starting point for a long marriage is 50/50. There is no magic formula to use, just the law as described and the judge’s absolute discretion on the final decision based on that law.