Decathlon do a good range of lightweight tents or some of the Vango ones aimed at backpackers.
I think Alpkit are launching a new range at the end of the week so you may want to look at that.
I use a Lunar Solo tarptent from the states. It’s a cracking tent but a bit pricey and you need to get it shipped over. Plenty of room for one person though.
I wouldn’t discount the lightweight side of things. If you save a kilo on a light tent – that’s the equivalent of a summer bag and an air mat.
For my setup, I have the Lunar Solo, a NeoAir X Lite mat and a cheap Lifeventure summer sown bag (replacing it this year with am ultralight quilt). Tent and mat in the seatpost bag, sleeping bag and clothes in the handlebar dry bag. Tools, tubes in the frame bag and a bum bag/waist pack carrying electricals, cycle jacket, wallet etc:
[url=https://flic.kr/p/o6Ad7W]IMAG0312[/url] by DKNWHY, on Flickr
My tent is on the left:
[url=https://flic.kr/p/o6pGye]IMG_1192[/url] by DKNWHY, on Flickr