The most important question is what you are going to hunt and where. You allude to not climbing mountains or going more than a couple of miles, but no mention of game.

In general, for what you have spoken of in general terms, I believe I would get a good .270 or 30-06 and call it good. Either in an 8 1/2# scoped rifle would be pleasant to shoot and effective. I’d probably not want to shoot a brown bear with either, but I surmise this would not be on your agenda.