I'm just going to go word by word here:
慰め (nagusame) has to do with comforting someone who is grieving or suffering, and is almost certainly not what you want.
便利さ (benrisa), also
利便性 are words that describe the most standard meaning of the English noun convenience in the sense that being able to walk to work is convenient.
However, it doesn't sound to me like you're talking about either of these things.
Imagine like you sit in a brand new car you’ve never seen before; yet, you intuitively know what is what and feel comfortable using it from the get go.
Here are the three phrases I would be inclined to use for something this (all three are usable like adjectives):
使い心地がいい (tsukaigokochigaii) literally means "comfortable to use". Of the phrases here, this one focuses the most on something feeling good to use.
使い勝手がいい (tsukaikattegaii) is often translated as "easy to use". This has more nuances of the tool functioning well, or it being easy to be effective using the tool.
使いやすい (tsukaiyasui) just means "easy to use" in the very literal sense of being easy to operate or understand.
Note that all three of these are constructions using the verb
使う for "use", and that #1 and #3 can be made with almost any verb. There is a brief explanation of the differences between #1 and #2 here in Japanese.