Don't waste your time with oem kit, trust me. The monsoon is an active system so will be much better but you'll need to change speakers and wiring.... I expect this will be more expensive than going after market.

I suggest you get a good quality pioneer or alpine head unit, not the cheapest one at halfords! Second hand is a good way to save cash.. You will find you need to swap the red and yellow wires round but this is done on the harness that comes with the headunit, dead easy and may be the reason you had trouble the last time.

You can get the amplified antenna adaptor for a few quid on eBay.