Getting an HPS light for budding

I have previously been growing autos with dual spec cfls, but now I feel like for tighter denser buds I need to buy an HPS.
1) What kind of wattage do I need for just 2 autos in a small closet grow (I don't want to much heat build up)
2) Right now I have a reflector with a 125W cfl in an e40 screw fit - can I just replace this with an HPS e40 bulb , and hook up a ballast to it? Or should I buy a bulb/ballast/reflector set?

Link me some options guys! I'm currently browsing amazon ; is there a better site for a uk grower to check out for some sweet grow lights?

Cheers

I'd look into a 400 electronic dimmable ballast gives you the option to dial it down to 50% if needed or go super lum for that extra. you don't state what size your closet is or what kind of ventilation you have or what your budget is. I just snagged an Ipower 600 off of E-bay for 31.75 plus 15.00 shipping. its a refurb so a bit of a risk. but on my limited budget I gave it a shot. Ipower are low end but people tend to give them a good report. I say take your time and research them good and not be in to much of a hurry. I don't believe you can put a hps in that reflector without rewiring. if your worried about heat I say get a cool tube. hope this helps some, I'm sure others will have a different opinion for ya with better ideals.