If you just want a corner shelf, I have used this one a few times and really like it. Can only get it from German amazon - not too expensive but the postage adds to the cost. It is well made and lightweight and fixes to the cage really easily. It would work well sitting just above one of the houses linked above - then you have two shelves and they like sitting under one and nesting in the house. On its own it might not be big enough to nest under - a bit smaller than the Savic shelf you have.
https://www.amazon.de/gp/aw/d/B008OQ...Q6PCDDEQ&psc=1