Problem with LED ones they are not as good as halogen in light. Unless you buy the super expensive ones and they can come in around £30 a bulb.
The other option is the CFL bulbs so bit like enegry bulbs. Do take a bit to get to full brighness but last long time and generete very little heat.
I will look into the underlay I think it will be case of whats the cheapest.
New set of down lights and rock wool or the underlay.
If anyone is interested the ones I'm looking at are this range