I think you're doing great explaining things to him. My dad died when I was 4 and nobody even told me he died! I'm the youngest of eight. My mom went in her room for like a year and my sister Kim took over parenting. Then my mom attempted suicide like 7 times. I was between the ages of 4-11 through that.
I wish my mom would have explained to me what happened. My dad died of a heart attack. They just put me in the bathroom. I think you're doing so well letting him go through his own grieving process.
About child therapists. I found a really good one for my son when he was younger. But it was mainly for behavior problems. I have hope you'll find someone.
You're a great mom!