Okay, so this isn't legal advice. You'll need to speak to a lawyer directly for legal advice. This is just some information to get you on the right path.
In terms of what you can do, while ever there are no Court orders in place, both you and mum are basically free to do whatever you want. Since mum has the child and her idea of doing whatever she wants is to withhold said child, then it's in the child's best interests that you get some parenting orders in place as soon as possible.
You've done mediation, that's the first step. From here, you'll receive a s60I certificate that will enable you to file an initiating application for parenting orders through the Court.
If you don't qualify for Legal Aid and hire a really expensive private lawyer instead, it can cost a limb, though probably more in the vicinity of $20-30k, rather than $50-60k. If that's above and beyond your allowance (which, let's be frank, it usually is), then you can consider self-representation as an affordable alternative.
Why should you consider representing yourself, aside from it being significantly cheaper for you?
Well, first, because the legislation and therefore, the Court, supports shared care.
Under section 60B of the Family Law Act, children have legislated rights to know, spend time and communicate with both parents on a regular basis, regardless of the status of the relationship between said parents, and insofar as the best interests of the children can be met. The entire Act pertaining to parenting orders is based on this right, so if your son is not spending time and communicating with you at present, then it's the Court duty to uphold his right to do so, provided it in the child's best interests.
Next, there's the presumption of shared parental responsibility. The legislation holds that the Court must presume it is in a child's best interests for both parents to retain equal, shared parental responsibility, which means that the Court must accept that it's best for the child if both parents are involved in major, long-term decisions affecting the child's care, welfare and development, in circumstances where the presumption has not been rebutted.
If shared parental responsibility is upheld, then the Court must consider whether equal care arrangements are in the child's best interests, and failing that, it must consider whether substantial and significant time with the non-resident parent is the next best option. Substantial and significant time is defined as a combination of weekdays, weekends, holiday time and special occasions (which is generally accepted to be more than the archaic every-other-weekend arrangement that Courts favoured before the 2006 amendments to the Family Law Act).
Whatever orders the Court makes, however, the children's best interests must be paramount. When determining what's in the best interests of a child, the Court is guided by s 60CC of the Family Law Act, which is a composition of two primary considerations, and about 12 secondary considerations. The primary considerations are the benefit to the child of having a meaningful relationship with both parents, and the need to protect the child from harm caused by abuse, neglect or family violence. The need to protect the child takes priority over the benefit of having a meaningful relationship with both parents.
So, what does all this mean for you?
In short, the legislation favours your son spending time with you, so if there have never been any issues of abuse, neglect or family violence, then the Court really has no reason not to make parenting orders accordingly, in most circumstances for five or more nights a fortnight.
The biggest hurdle parents face in getting such an outcome, however, is being drawn into conflict with the other parent. Any parent who can behave amicably and remain child-focused, even when the other parent can't, stands an exceptional chance of getting parenting orders in their favour.
As an added note, unless there have been issues of domestic violence or similar in the past, then the Court doesn't look highly at all on parents who withhold their kids from the other parent and who refuse to include the other parent in parenting decisions after separation. Such behaviour is rarely considered to be in the best interests of a child.
In short, you should consider filing an initiating application with the Court. About 95% of cases initiated in Court actually end up settling by consent, so the likelihood of you having to go to trial is actually fairly minuscule, and just as you can't afford a lawyer, it's very likely that neither can mum, so she's probably going to be more open to negotiating an agreement with you in order to avoid a looming Court date. Even as a self-represented litigant, you have a very good prospect for success, provided there are no issues with domestic violence or similar.
In my experience, fathers always get a better outcome once the Court gets involved than if all they do is try to negotiate an agreement with their ex....
