Hi Craig,
Not too sure whether they will fit, but I would go for a set of jbl's

(the small ones think theyre gts or gto).

I had a set in my old car and you couldnt beat the sound quality and that was also on a 4x50w sony.

They are a tad pricey

<£80

but like most things, you get what you pay for.

Failing this I would go for a set of pioneers

<£50.

There's a couple of posts on this forum that give speaker measurments somewhere.

Think the depth of the magnet is around 50mm and the diameter of the speaker should be around 6" not 100% sure so I would check 1st b4 buying so you avoid modifying your doors!
Cheers
Dan