Getting sole custody/responsibility of my child

I am hoping someone may be able to assist with my query with regards to sole custody/responsibility of child/children. When I completed the petition I originally filled in the child arrangements form for my husband to have my son every other weekend. Unfortunately certain things have come to light and I would not be happy for this to now happen at this moment in time.
My husband has verbally agreed that I can have sole custody of our child so long as I do not prevent him access to our child. I have no intention to prevent access, but would not feel happy at this time for my husband to have him all weekend.
Can someone best advice how I go about getting sole custody/responsibility of our child. Is it a case of having an agreement drafted by my solicitor, will this be enough.
Where do I stand on going abroad on holiday, will I still require husbands permission if I have sole custody/responsibility for our child?
Any assistance would be greatly appreciated.

In most cases there is NO NEED for eithe W or H to have a Residence Order (Custody)

Both parties have PR (Parental Responsibility) and equal rights

"Unfortunately certain things have come to light and I would not be happy for this to now happen at this moment in time." what are the brief concerns?

I believe you are approaching the issue the wrong way.