So you are looking to replace the MicroMV cam with a small DV cam?
The IP55 is 125x39x92 (mm, W x H x D).
Sony used to have some very small DV cams, like the PC55 (which claimed to be the world's smallest). The current DV models are all small, but not quite as small (e.g. the HC 46 is 65x79x113 - a different shape to the IP55).
It would depend on your price range, and what features were important (and just how small it needs to be).
Looks like you can still get a PC55 starting at £350... this is 45x99x72.
http://www.pricerunner.co.uk/sound-a.../315558/prices
Mark