You can't replace normal wall light switches with Smart Switches in the UK because of the way they're wired. LightwaveRF make a Smart Dimmer, but that doesn't work with the Echo without IFTTT (I don't know if Yonami will control it?)
Luckily this is not true, you can replace wall switches (standard and dimmers) with smart switches. There are a few systems around and some brands use the same technology meaning you can mix products from different manufacturers. But they not the best idea for a beginner.
http://www.vesternet.com/smart-home/lighting/modulesThe Harmony Smart Hub will control the TV and all your devices, but it will require something to "bridge" the Echo to the Harmony. Yonomi would be the easiest option for now. There are better solutions out there that bridge the two, but they do require a fair bit of technical knowledge. Remember that IFTTT is coming, so it might be better to wait.
It is worth thinking about what voice controlling your TV will give you. You usually use your thumb to control things, and it is easy to press press press. With voice commands you would have to say (hypothetically) "alexa, press tv button up", "alexa, press tv button up", "alexa, press tv button up". You will quickly be kissing the physical remote asking for its forgiveness
Yonomi can (for now) only fire up an activity in Harmony, which is very good in itself. You say "alexa turn on Movie Mode" and the harmony turns on the projector, the amp, the apple tv, switches the amp to the right input, dims the lights (if hue). Then say "alexa turn on Smart TV" and the projector turns off, the tv on, the amp off (or on and changes input) lights come up to 50%.
It takes time to master it, but if you are looking for a new hobby then it can be rewarding to engage smug mode when it all works
For lights, then Hue. It is great, the colours are super rich and there are a million apps and devices that work with it.