He sounds adorable <3
Yea pets at home cages are not very big when you start to realise what hamsters actually need. A lot of people recommend cages from Zooplus (the Alexander or Barney I believe) and are not to expensive compared to pets at home - currently on offer too! They have lots of offers on toys and cage accessories too.
I have a DIY cage which you can find lots of tutorials on youtube for. Similar price to shop cages but bigger. Just depends on your finances and resources really.
Sounds like your doing an amazing job and he is going to be one spoilt hammy
Enjoy playing with him and hopefully many snuggles to come!