I’d just go with whatever you like best and not worry how it sounds. Full names are so rarely said aloud and apart from when the baby’s born and you announce the name, nobody really cares. My children both have two middle names to honour relatives. It doesn’t matter to me how they sound, in fact I’ve not really thought about it til now!
That being said both choices are beautiful and Mabel and Matilda were both on my girls names list.