There are loads of threads about travel systems and be warned - you could drive yourself absolutely mad with the choice!
We bought an all-singing all-dancing monster-truck of an all-terrain pushchair with car seat fitting. Looked great, very trendy, etc. but an real pain in the a*se. Soooo heavy I nearly put myself back in hospital getting it in and out of the car. This time round I've bought a 2nd hand mountain buggy (from a mumsnetter!) and a matching carry cot off eBay.
Advice I would give is to try and get as light a pushchair as you can - the lightest are Jane Powertrack / Mountain buggy /Bugaboo, and all have carrycots but are v.expecnsice (around £500-600). The advice these days is to not use the carseat for any length of time as the baby needs to be flat - it's better for its back. You also need to think about what you will use it for. Will you be doing lots of walking, incl off-road/countryside/parks, etc. or will you either drive most places and use the pram for town shopping, etc.?
Also be warned that you may well find the travel system so cumbersome that when your baby starts sitting up you go out and buy a buggy for £70 and the old pram ends up taking up loads of space and turns out to have been a huge waste of money. That's why getting a light/narrow one is a good idea, so you carry on using the pushchair loads when you get rid of the carrycot. Some can also be used from birth in their lie-flat positions.
Have a look at the Review section on Mumsnet. As a guide for weight, anything less than 10kg is good going, but that might not matter so much for you if you're not getting it in and out of the car or trying to wedge it between narrow shop aisles.
Good luck!