Sleeping space and activities
A 16-week-old kitten still sleeps a lot, and you have to respect its sleep and leave it alone when it sleeps/rests.
Cats like to sleep up high, and although few people think that cat trees are pretty, they are smart because they fulfill several functions. Choose a tall cat tree with a large hollow, good thick scratching trunks, large hammocks and a cozy basket at the top. The cheapest cat trees do not last long - Zooplus.de is somewhat cheaper than the Danish Zooplus. The selection is the same and they are good solid trees. Decide from the beginning where the kitten can be ... if it is allowed to be in the bed, on the sofa and on tables, then that is what it does. Cats can be very persistent and insistent, but they can learn anything - even that they can lie on a blanket on the sofa. Move the kitten quietly to where it needs to be. Choose a sound that is easy to say and use it when the kitten does something good or something it wants to, and maybe supplement with a small treat.
Brits are often hot, so they love to lie in the bathroom sink. They also like to lie stretched out and preferably on their backs. If you have to transport the kitten (e.g. to the vet, in a holiday home etc.), it is a good idea to offer the transport box as a place to stay, so that the kitten is used to the box. When the kitten is awake, it needs to be activated/played... most kittens can't handle teasing sticks, felt balls (the Grene sisters) are a hit, activity boxes, where they have to fish out treats, are a hit. Cardboard boxes with holes are also a cheap toy. Small soft balls that bounce, various small stuffed animals with catnip are also nice - play with the kitten, but also let it play/activate itself. With small soft treats as a reward, you can teach it: to come, to get things, to give "High five" and much more. The more the kitten is activated, the more nimble and active it becomes. Adult Brits also like to play, so keep the activity going if you want a cat that does more than sleep. Britten is a muscle cat, and it doesn't get muscles from lying on the sofa..