Cassette players are becoming rare beasts these days. CD's have taken over a bit.
I've had a quick look on Amazonhttp://www.amazon.co.uk/s/?ie=UTF8&keywords=audio+cassette+player&tag=googhydr-21&index=electronics&hvadid=3397845125&ref=pd_sl_8r5rmwrlzx_b
(copy/paste the whole lot into your browser)
If you can't get the link above to work go to www.amazon.co.uk
and look for audio cssette players in the Electronics section.
They do a cattette only unit but I'd watch out for sound quality if hearing is an issue too. Advantage - fairly simple to use.
There are a lot of "walkman" style units but the controls will be smaller and you have to use headphones.
Next in line is the combined unit which will do Cassettee, CD and Radio - if you go for a reputable make like Sony or Philips then they'll have stereo sound which will be and improvement over the cassette only unit. Most of the units are fairly straightforward to use and if you use it in one mode only - cassette for example then it should be a matter of switching the unit on and hitting the play button.
It's well worth shopping around once you identify something suitable as there is a big variation on prices on the net.
Hope this helps