Need some help/advice re best battery for me to get.

I have had some problems with the battery draining quickly and then lacking sufficient power to crank the engine (car used very rarely) - it will start on jump leads and will run fine but to be honest I think the battery is shot to bits.

1) I have been hunting around and it seems I can get either a 650 CCA (cranking) 72Ah or a 590 CCA 60 Ah battery - again I assume best idea is to get the 650CCA 72Ah battery?

2) Am i right in saying that I should get a trickle charger to keep it topped up when I am not using the car?

Any help appreciated as I am certainly no expert when it comes to batteries.