Much easier for a robo as they're so little and aren't that bothered about toys
The labyrinth house would go down well (our robo has a labyrinth house). They mainly like tubes and tunnels and hidey places and a shelf. And a wheel and flying saucer. Our robo has a 9" wheel and a 7" flying saucer and uses both. He also likes the little hay and carrot cottage and spends ages in it scraping the hay off.
If postage is cheaper from Amazon then you can get most things there. Either of those Trixie wheels in the 8" size would be good. Here are a few of my favourites from amazon!
This is soft and chewable and has lots of holes in
https://www.amazon.co.uk/Rosewood-Bo...h+tunnel+small
Cheese cube - this is popular with robos - check for any sharp bits and sand if necessry
https://www.amazon.co.uk/Rosewood-Bo...er+cheese+cube
This is the carrot cottage
https://www.amazon.co.uk/Rosewood-Na...carrot+cottage
Our robo ignored all the little houses and just burrowed under the substrate - but when I gave him a labyrinth house he moved into it (nice and dark inside and mimics a burrow with rooms).
This is the wheel
https://www.amazon.co.uk/Trixie-Wood...s=trixie+wheel
And flying saucer
https://www.amazon.co.uk/Small-n-Fur...g+saucer+wheel
The other trixie wheel has quite large holes so I decided against in case they got hurt when jumping out and missing the hole! But the 8" wodent wheel has smaller holes and that's good too if you want a plastic one. You can hang those upside down from cage bars (attached with a couple of cable ties) which keeps them stable.
The picture is of the larger wodent wheel but the link is for the dwarf sized one (called the robowheel in Germany)
https://www.petplanet.co.uk/product....27&pf_id=52720
This is what the 8" one looks like. Wodent wheels are hard to find in the Uk
https://www.amazon.co.uk/20-Wodent-W.../dp/B014N5U26Y
Other than that toys like a cardboard egg box with a hole cut out or toilet roll inner tubes etc go down well
They do like a shelf or platform though.
I also use the rat sputnik for our robo as well - hung it next to his shelf so he can climb in - I put the odd treat in it so he goes in there and sits in the bedding sometimes.