What psu should I pick?



For slimline: http://pcpartpicker.com/mr/newegg/athena-power-power-supply-apmfatx35

http://pcpartpicker.com/mr/newegg/seasonic-power-supply-ss350tgmbulk

The 2nd one is a much better value - but might be a bit too tall, 2.5" vs 2.1" for the one in your machine.
Take a look and see if you have the half inch to spare.