We stayed at the Big Sleep for four days and couldn't have been more satisfied of our choice.
Location is unbeatable, with all major Antwerp attractions close by (Historical center, Fashion district, Het Zuid, Sint-Anna Tunnel...), yet the area is semi-pedestrian and extremely quiet.
The flat is very stylishly furnished, has great audio / video and unobstructed views as it is facing a small street.
Finally, Myrthe lives in the building and is very responsive and helpful.
All in all, the place to stay in Antwerp !