Within your budget, the Four Points is supposed to be one of the best anywhere. I stay at the San Cristobal Tower (the LC part of the Sheraton).There is a nice pool and gym there. Either the Four Points or Sheraton/Tower are in good locations, and metro close. They are also in very good neighborhoods - safety is no concern at all other than common sensibilities. Also, taxis are abundant, inexpensive, and safe.

Spanish is the language, but the dialect is notably different than what you may be used to, and many words, including many foodstuffs, are different. Argentina is even more different.

Also, I know you aren't wanting to rent a car (and driving in Santiago isn't a good choice of pastimes), if you want to wind down some more, you might consider renting a car to drive out to the coast - it is a lovely drive on a new-ish toll road and takes about 2 hours.