The problem you have at the moment is many many IoT manufacturers developing with various different standards/protocols either don't work or don't integrate well with others.
As far as i know, there are no manufacturers that offer everything under the one app (you can get very expensive solutions, but these aren't necessarily "smart"). This is really where open-source has come in - Home Assistant and OpenHAB are probably the two main contenders that allow you to have a central hub for controlling - more on that below.
For light bulbs, Phillips Hue are the ultimate leaders for smart lighting, they now have a wide range of products from bulbs, to ceiling lights, mirrors, external lights, strip lighting etc. They are generally quite expensive though (look out for Black Friday deals etc) but you typically get what you pay for.
There are other bulb manufacturers that can be controlled as part of the Hue app, one of the well known ones now is Ikea's Tradfri lighting. These tend to be significantly cheaper, although don't have quite the complexity that Hue does. So for example if you're after a standard bulb with just the ability to vary the brightness then Tradfri bulbs are certainly worth looking into. The Hue bulbs can give you colour and white temperature along with dimming.
Hue has originally come with a hub known as a bridge to control the bulbs, i believe the generation released this year now has the ability to control them all via bluetooth, in order to compete with other bulb manufacturers. Personally in my opinion, if you're planning to have a reasonable number of bulbs, then get a bridge.
Smart plugs are something that Hue doesn't specialise in, i did hear there was a LIFX smart plug that could be integrated with the Hue app, but at the time i looked LIFX didn't offer any UK sockets. I've currently got a mixture of TP Link plugs that have energy monitoring, and a brand called Meross, who also offer smart 3/4 gang extensions.
Back to the smart home hub, i've personally favoured Home Assistant over OpenHAB just because there seems to be more of a community of developers behind HA meaning more stuff generally works.
The problem with these solutions is that they are not just a "plug and go", and being open source they require a lot of tinkering to set up. However when they work well, they work very well.
Take a look at some of the dashboards that people have put together here:
https://demo.home-assistant.io/#/lovelace/0
There are lots and lots of components that you can use to make your home smart.
Ideally you need to sit down and decide, firstly what your budget is to be (you can end up spending lots), and secondly what are you after, and for which rooms.
