Going forward, the 737-800 is favourite to replace the current fleet.
Yep and despite obviously having a 737 fleet now, im surprised they wouldnt infact be looking at Airbus seeing as though it's the way it's big sister and big mother airlines have gone. I know in past twitter interviews that this has also been the case to look at newer 737 aircraft so sounds like they are finally on to it!
As for the 738, it will be a great aircraft for bmibaby, however it would be interesting to know if they would also be looking at the 73G aswell for the shorter/higher frequency routes such as UK domestics and AMS etc, where the 738 could be too big for them.