If you take the green shelf out you'll have room for the bigger wheel
My cage is virtually the same as the hamster heaven and there's no room for hammocks lol. Although maybe in the front left corner, with the wheel in the back left corner. I had that for a while, but be careful with rat hammocks as hamsters can chew fleece or material and it can cause blockages. I had a lovely fuzzbutts fleece hammock in and had to take it out again when Charlie started chewing it, so I got a rat sized sputnik instead. These grass hammocks are ok though.
Natural Grass Hammock for Pets at zooplus
Same one at Amazon
Rat hammock Grass 40 x28cm: Amazon.co.uk: Pet Supplies
Did you get the 28cm wheel?