I have used Skandia, who have an investment vehicle that allows you to invest in a wide range of funds and therefore fund managers. It also allows you to swap between funds and fund managers at minimal cost. I think it is now called Multi-ISA, it used to be called Multi-PEP. As I am sure you are also aware investing in "funds" does spread the risk against investing in single Companies.
Only you however can decide which funds to invest in. Your decisions on which fund to use will be dependant on your attitude to risk, and if you want income or capital appreciation. I have used several "execution only" brokers, including Hargreaves Landsdowne, who have not charged for up-front advice, but have taken trail commission. This is, as I am sure you are aware is changing.
I tend to read the financial press before deciding where to invest. At the end of the day however there is no real way of avoiding the buy/sell spread, so you have to wait until the price you sell at is higher than you bought at, a hidden cost. If you are willing to look at the long term, 10+ years that should not be a problem. Good luck.