I did that last year. A few tips:
British Airways and American Airlines are partners. If you have any miles for American Airlines, or have a credit card that rewards points for them (American Express does), you can fly roundtrip from London to Paris for 15,000 points. It's much quicker than taking the Eurostar. Additionally, sometimes British Midlands runs airfare specials, and that can be cheaper than the Eurostar.
As for hotels, your best bet is to stay in Paris and take the train to Disney. The train stops right at the gates of Disney, and is about a 45 minute ride from Paris. If you do this, you can save money by staying at a hotel in Paris proper, rather than at Disney.
Also ... you can't negotiate on a park pass from
Disneyland Paris. For instance, if you stay at a Disney hotel for 3 nights, you must get a 3 day pass. So, if you wanted to spend a day sight seeing in Paris, you still have to get a 3 day pass. I don't think they sold hotel rooms without a pass. It turned out to be much more expensive than staying in a hotel in Paris and buying park tickets.
And, lastly, the Studios over there are not that great. I don't know what the reviews are lately, but when it opened, it was admittedly a disappointment.