Lets "assume" your vehicle was new, then adding a winch bumper would most likely not affect it that much, but because its not new, the springs would have sagged a lot, possibly as much as an inch........and over time they get weaker in their "rate" so the additional weight of the bumper will make a considerable difference, add a winch into it, which is going to be around another 35+ kgs, then it will droop even more.
Land Rover produced "winch springs" for vehicles that had the factory winch kit fitted, they provided no lift, just a "stiffer" spring rate to compensate for the front mounted winch, and that never included a heavy duty bumper, just the winch and a tray. You will notice the additional weight more when braking as the nose will "dive" more with the addtional weight.
So in a nutshell, anyone who adds a winch bumper of any type should always up rate the front springs, whether you do it with standard height or lift springs is up to you.
As far as a specific "kit", what you have been told is bull**** tbh, there are LOTS of choices, and what works for one will not for the other. Any "lift" kit will basically consist of a heavier duty spring as thats how they achieve a big proportion of the lift.
What you have decide is what your budget is, you could do the whole car with springs and shocks for not much more than £200, but you could also spend that on just 2 shocks..........
Buy the best you can afford at the time, because buying "cheap" normally means you end up buying twice.
