I'm not sure attracting a top player will necessarily be a huge problem - we may well be planning to sell Laporte next summer when he has 2 years left, as he's shown no signs of renewing and has made plenty of noises in the last couple of years.
Kounde would be ideal - not only as a top centre back, but also an alternative and potential successor to Walker. We know how vital Walker's pace and defensive ability is to our side - Kounde would be a far more solid option there against top sides than Cancelo IMO.