Hi and welcome, i too have ibs-d and find the mornings to be my worst. The only thing i can say about fibre supplements is that you have to give them a go to see if they wil help you. Fibre is a regulator so its good for both C and D, if you can tolerate it. I, unfortunatly, can not. You may need to try different types of fibre, ask at the health store or google for different types. When you do try, ignore the dosage amounts on the tub and start off real slow, kinda ease yourself into it and drink a ton of water daily.
One fibre supplement that i was ok with for a while was FibreGel. Comes in lemon or orange and you take a sachet after eating. This was the least agrivating suplement i tried and worked for a good couple of years before i sort of became immune to it.
Other things you could try is making sure you have a routine. Get up at the same time every day, even weekends and your tummy could get used to goibg at roughly the same time scale daily. I need 3 hours to get ready in the morning before i am comfortable enough to leave the house. Do not eat late at night either, and excercise in the AM may help. Lying on your back with legs in the air doing cycling motions is very good as it actually massages your tummy inside and can be calming.
I hope this is of some help to you.