Hi D.,
I can't help you on the job front, but I know a little about child support, since I just got a court order for it a couple weeks ago.
I am a supporter of child support being paid through ths state.
The advantage of going through SDU (state disbursement unit) is that your son will receive the amount he is supposed to (generally 20% of his father's income), and if your ex gets an attitude, you won't have to worry about him ever paying. The state takes the child support directly from his paycheck -- though it's not viewed as a garnishment. Your ex will have proof it was paid so it protects him, too.
Because you are already in the state's system, they will work with you to collect child support. You can visit IL's Child support website at http://www.ilchildsupport.com/
You can also go to a consult with a private attorney to find out what your options are. MOST private lawyers offer a free consultation. You can find a lawyer through your county bar association or through referrals here on Mamasource. WILL COUNTY BAR ASSN: http://www.willcountybar.com/
You seem torn because you feel your ex would pay the child support willingly. This may be true, but you never know what the future will bring. Generally, for one child, the father has to pay 20% of his income. Did you know that Illinois also allows for the father to pay a percentage of the daycare expenses, in addition to child support?
My ex has to pay child support and the court also ordered him to pay 48% of my son's child care expenses. It might sound like a lot... but raising a child is expensive. The amount of money I get for my son between daycare money and child support gives me enough resources to know I don't have to put my son in a hovel for a daycare and that I don't have to worry about him not having enough to eat or clothes that fit properly.
Just remember that whether you go through a lawyer, the state collecting for you, or privately -- you are your son;s advocate and have to speak up for his needs because nobody else will.