HR Strategy for PTO and Parental Leave Policies

My NPO does not currently have a parental leave policy and our PTO policy is lacking for most employees. We are trying to sort out how best to provide parental leave for employees while being mindful of the expense that comes with employees being out of the office. Currently we don't have any parental leave and most employees only receive 10 days of PTO (we do not differentiate between sick and vacation time). We are a small NPO (only 10 FTE and 1 PTE), so time off is difficult for the team to manage. All of our staff are in their childrearing years and we want to retain our staff with these benefits. We currently offer 70% reimbursement for STD but this is insufficient due to duration and doesn't provide support to a non-birthing parent. We consistently face a budget deficit and this is a very big concern for our board. They are in support of a parental leave and more PTO for staff but are concerned that time off will lead to a larger deficit. The Board is seeking numbers/data to support a policy and despite having a committee of board members and staff examining this, we don't know how to find information to support a policy that won't have a significant impact on the budget. Annual budget is $1.6 million. Last year's deficit was $94K.