Can anyone recommend a decent, portable digital recorder for making field recordings?

It seems to me that the market place has a bewildering array on offer.

Ideally, as I'm too old to learn the multiple skills of a recording engineer, what I'd like is a small, simple-to-use device that could be placed on a table and, with one click, record what tunes are being played in a quality that will make them listenable and worth saving for posterity.

I know these things can be expensive but, although cost IS an issue for me, I'd be happy to pay as much as it takes to ensure the recording quality is high enough to make them worth preserving.

I am happy to buy secondhand.

As a secondary consideration: in which format(s) would mudcatters suggest recordings be preserved? Presumably, if the quality of the original is high enough, it should be a loss-less format?

Will an mp3 file be generally playable in 5; 10; 20 years time?

All advice and thoughts gratefully received,

Harry