HELP with Discretionary Leave

I recently received ILR. My partner and I want to get married, however, he overstayed on his student visa in 2006.

I have just found out about discretionary leave to remain and considering applying for him. However, we have been advised that he should return home, then I can join him in his country and get married there. Thereafter, I can apply for him to return to the UK.

We have an 8 year old child together who is not in the UK and we have lived together in the UK for more than 5 years. We are not the same nationality.

As we are trying to save on cost, could we apply directly on our own to the Home Office. And what are the chances of success without using a solicitor.

What kind of evidence would we be required to submit? which forms to use?

Any other info which you will consider useful will be appreciated.

Thanks for your time