I usually have some latency between when someone says something and when I've finished running my "Am I about to say something stupid, pedantic, incorrect, boring, or cruel?" checks on my response. In my experience, removing filler words makes people think that you weren't listening to them or aren't going to bother to responding to what they said. I've had to deliberately practice saying "umm..." before speaking rather than just being silent while I thought about my response.
I do a lot of public speaking, presenting and demoing to audiences of various sizes, and am considered (by at least some people) quite good at this stuff.
My advice would be just stop and think when you need to. It's completely fine and you will convey the impression that you are a serious and thoughtful individual, which is good. You can show that you were listening and are about to respond entirely through your body language.
If you feel uncomfortable with that, there are a bunch of simple tricks you can use here and saying "umm..." is not a good one. One easy thing is to always ensure you have a glass/bottle of water. If someone asks a tough question and you need time to think, wait until they have finished their question, then take a drink of water. No-one thinks this is even slightly strange and it gives you time to think and make a considered answer.
Forgive the expression, but I usually take a multithreaded approach in those situations. For example, you could (probably) easily rattle off a meaningful but neutral initial response and, while you're doing so, run whatever filters you need to before you arrive at the meat of your response.
Almost, I failed to mention the reply should contribute something and not just be words for the sake of words though. Purely my personal opinion. Basic example of a borderline canned reply while I think:
Q: "Where should we host our service?"
A[instant]: "Well, you have X, Y, and Z."
A[afterwards]: "X has these features, but Y might be a better fit for you because..."
An easy one is just acknowledging that you heard the person. Mix and match: oh, ok, huh!, (rephrase what the person just said), I had/hadn't thought of that, cool, interesting, that's an option.
