https://www.parcel2go.com is a lot cheaper than ParcelForce and is still fully trackable (they use DHL). Definitely worth weighing it and adding courier costs to your listing as you will get more interest and a better price. It costs about £8 per item up to 25kg.
It'll certainly be less than 25kg. DH weighs himself on bathroom scales, then weighs himself again holding whatever it is and then subtracts one from the other. We've managed that even with huge pram boxes etc.
SparklyGothKat has a good point about the insurance. DHL (via the parcel2go website) only provide £50 insurance for free but have the option of adding extra insurance - I've never bothered but assume it would still work out cheaper than Parcelforce. Having said that, on a high value item like a Bugaboo buyers probably don't care that much if postage is £10 or £25.