I would call a few family solicitors (assuming that's the area this relates to), give them a very brief summary of your issue and what you need from them and ask for a quote.
If you want them to confirm what you've said sounds reasonable (so you don't get penalised if it ends up in court later) and that you're not saying anything that might be detrimental to you later from a legal perspective (for example, agreeing to something that sounds innocuous but actually could have legal ramifications and prevent you from asserting your rights later), remember that you're not just paying for the value of their time in familiarising themselves with your case. The value they provide is in their up-to-date knowledge of the legislation, case law and their own professional experience of how courts treat various scenarios and what the potential pitfalls are.
I'm a qualified solicitor in another area of law, and knowing how much emerging case law and random bits of legislation there are that my clients would have absolutely no idea about, I always get family law advice on my personal family law issues. It has proved hugely beneficial, both financially and otherwise.
Before you ring round, it's worth considering what outcome you're hoping to achieve and what might be acceptable as a compromise position, so they can manage your expectations and/or help you achieve it. You can usually get a feel for someone quite quickly once they start talking about your issue.
Plus, I often find that they mention things I haven't thought of so it's a helpful exercise even if you don't end up instructing anyone!