In general, it's always a crap shoot. You never know how someone is going to take the news, just as you didn't know how your mom would react. The fact that your mom reacted in a non-negative way is worth something, but the fact she loves you no matter what is just.......wonderful.
I didn't have to tell a parent, as my mom and dad passed away more than a decade ago, and we're not telling my spouse's mother. She's in a nursing home, has Alzheimer's, and the last thing she needs is information she can't process, or handle.
Our kids and grandchildren live with us. When I told Marcy, she was totally supportive, knew I had a soft female side, but had no idea I was trans.
When we told the kids, they said they already kinda knew, saw some differences, and was giving me time. The grandchildren were told by their mom and dad, and they're fine. The last couple years I've been their other grandmother, Nanna.
Someone stop me from rambling!
Bottom line: my opinion is to let your mom tell your dad, then talk to him and answer his questions when he is ready. If that is too long a time, then approach him. Whatever happens, I'll bet your mom breaks the news to him herself anyway. That's how parents operate.
I wish the best for you
Bev