Depends on what you want, what you have available locally and if you are willing to buy blind online.
For a planted tank I wouldn’t recommend anything other than a soil type substrate now but it is rather expensive. I’m using the tropica one but the ADA, JBL, Fluval etc versions are all fine. For a small tank I would get the smaller grain size for tropica it’s referred to as ‘powder’.
As for rocks/wood you really are limited to what’s available unless you want to buy online and this is typically blind so you don’t know what you are getting. In my experience most local stores are pretty poor when it comes to decent rock and wood.
Also if you are going planted I would suggest a rimless tank but again these are more expensive but the tank it’s self wont dominate the room as much because they don’t have thick bezels, lids and use clear silicone instead of black. They also make the content of the tank stand out much more.
I have a Denerle scapers tank which is nice. Aquarium Gardens also have a line of small rimless tanks which are rectangular rather than cubes.
https://www.aquariumgardens.co.uk/glass-aquariums-98-c.asp
I have this kit which is a good starter kit:
https://www.aquariumgardens.co.uk/dennerle-scapers-tank-complete-35l-led-1548-p.asp
It comes with a basic light and filter which are fine for low demanding plants, you just need to add a small heater. It also has a lid but you don’t need to use it, if you run it without the lid you can get creative with bits of wood and plants coming out the top.
George farmer also just did a Fluval Flex setup with everything bought from pets at home, it’s worth a watch. Search George Farmer on YouTube.