Premier Access Ultimate or Premier Access One?

My family and I are going to Disneyland Paris for the first time in July, probably on July 10th, a Friday.

We're unsure whether to buy the Premier Access Ultimate. Looking at the selection of rides, some seem a bit silly, and we wouldn't necessarily want to go on all of them. Therefore, we're wondering if it would be better to buy the Premier Access One on the day of the park, for rides like Crush's Coaster, Ratatouille, Big Thunder Mountain, Peter Pan's Flight... but knowing that July is a very busy month, we're worried about not being able to get that option. Does anyone who has gone during that time know if it's easy to get the Premier Access One pass for these more popular rides?

And there's the issue of only being able to buy one at a time, right? What would be more worthwhile in our case? Some agencies provide a guide with you all day with the Ultimate experience, is that more worthwhile?

Any comments are welcome to help us with this decision :)