Take a look at the avionaut pixel pro and the avionaut cosmo - the pixel is the lightest seat on the market. Cosmo slightly heavier but still a very good and safe seat. They’re also compatible with most prams with the right adapters
Yes you’re better buying a pram you like and the car seat separate. Many that come as systems are fairly poor. As Fran said, avionaut cosmo or pixel are excellent and super safe choices
I got the maxi cosi pebble 360 pro2 and base for less than 500 - ive seen it in action with my nephew and love that it rotates and slides out on rails for better access