Unfortunately childcare vouchers were closed to new applications back in 2018. Besides, they were classified as employer support, so were not available to sole traders anyway.
However, there is a childcare element to working tax credits for which you may be eligible and you may be able to claim an extra amount to help cover the costs of approved childcare. You can find the eligibility information on working tax credits here and it covers things like the type of work you do, the business records required and any licensing or insurance in place.
The basic amount of working tax credit you can get is £2,005 a year in 2021, but there are extra ‘elements’ that can boost that amount. The details can be found at .gov.uk here.
For state contributions to childcare costs the main thing you have to do is ensure that any provider you use is approved. The details on this can be found here. Here is the link to the calculator to help you work out what amount of money you can get towards paying for ‘approved childcare’.