I know your husband doesnt want to ttc but have you asked how he would feel if it happend by accident? after all you are married and love each other and yes each child brings its own finnaical commitment but what are his reasons for wanting to wait so long?
my children are close in age 2 20month age gaps and it works perfectly for us we are happy for God to bring us another baby in his timing and we always talked about having a few children with smallish age gaps because of advice ive had from a doctor about my back in the past but both the second and third babies happened by surprise for my husband though God had spoken to me about it