Filler sounds in English
Solution 1:
There are quite a few "filler words" that can be used to indicate a pause for thought. Most of them are not real words, but are sounds like "umm", "mmm", "er", "uh" or "ah". This has lead to the phrase "umming and ahing" to describe someone having difficulty making a decision.
Sometimes people also use the word "like" whilst thinking, but this can annoy some people.
Solution 2:
In the States, we usually do "Ummm".
Sometimes, to emphasis a "no", we say with some sass "aaah..no".