Hi bigmumma, in family proceedings it is not uncommon for parties to act in person. From what you have said, your case is very straightforward so hopefully it may be resolved at the hearing on Wednesday.
In relation to these type of proceedings, there is the 'no order' principle in that the Court will only make an order if it is in the best interests of the child and if there is a dispute. Technically, if there is no dispute with your ex that your DS will reside with you, then there should be no need for a Residence Order in your favour. However, given the recent history, ie your ex took him and it took the involvement of solicitors to get him returned, you clearly want and need the security of a residence order. With this, if your ex were to do this again it would be far easier for you to seek to have your DS returned, eg you could contact the police who would hopefully get involved instead of brushing you of with 'its a civil matter, go see a solicitor'.
At the hearing on Wednesday, you and your ex would both attend a meeting with the CAFCASS officer. Even if your ex has legal representation, his lawyer would not be allowed into this meeting, so you would not feel disadvantaged by being in person. You would be asked why you are seeking the order and you would simply explain that you and your DS need the security that it provides, in case your ex tries taking him and not returning him again. Hopefully, you may be able to agree in that meeting that you should have an order and if so, an order could be drawn up and approved by the District Judge (DJ)
If you ex will not agree to this, then you would then go before the DJ who would then order CAFCASS to prepare a report which would involve meeting with both you and your ex separately and at your homes. You may be seen with your DS, depending on his age. The report will then be filed at the Court (usually within 12 weeks although in some areas it can take longer) and once you and your ex receive a copy of this you will have the opportunity of filing statements in support. The CAFCASS will give their recommendation in the report. The matter would then be listed for a further hearing before the DJ.
To be honest, I know quite a few people who have acted in person up to the stage of the report being filed and then depending on the contents, made a decision as to whether to instruct a lawyer. Hopefully, it will be resolved very quickly so you will be able to represent yourself throughout.
Alternatively, as IloveTiffany suggests, you could take a mckenzie friend with you. This is basically a layperson (unqualified assistant) who could attend the hearings with you and speak on your behalf. There are various groups around that can assist with this and you should maybe contact your local CAB or the County Court where the application is lodged to see if they can recommend anyone.
Good luck