I'll start by suggesting what NOT to buy:
There have been quite a few posts on AB (as well as in other web forums and in the technical press) from people who've found that there's not enough space on the hard drives (or solid state drives) of their laptops to handle all of the updates that Windows 10 keeps throwing at them. That's because they've purchased some of the cheap models which have been sold during the past few years (and continue to be sold) with only 32GB storage available. So I STRONGLY recommend avoiding such models. (i.e. 64 GB storage should be regarded as the absolute MINIMUM to go for).
If you're prepared to consider a refurbished laptop (from a company which I can thoroughly recommend), take a look at these:
http://www.accomputerwarehouse.com/products/computing/laptops-notebooks
(They would all be perfectly capable of meeting your basic needs but they might not be particularly light).
With a bigger budget, the ASUS ZenBook UX410 is the current 'Best Buy' in Web User magazine:
https://www.johnlewis.com/asus-zenbook-ux410-laptop-intel-core-i3-4gb-ram-128gb-ssd-14-/p3240701
That laptop weighs in at 1.4 Kg. The Acer Aspire 3 is heavier, at 2.1 Kg but it's got very good reviews and offers excellent value for money:
https://www.tesco.com/direct/acer-aspire-3-156-amd-a4-4gb-ram-1tb-storage-full-hd-black-laptop/659-7979.prd
In the same price range, at 1.9 Kg, the Lenovo IdeaPad 120S is also very well-reviewed:
https://ao.com/product/81a50028uk-lenovo-laptop-grey-56163-251.aspx
At roughly the same weight (and price), the HP 255 G6 has equally good reviews:
https://www.ebuyer.com/819846-hp-255-g6-laptop-3ky08es-3ky08es-abu