It's not as simple as "add it to your cost basis" makes it sound.
If by "decorate" you mean staging costs, that should be included as part of the RE agent's commission. If it's not, then they're included in selling expenses.
Your new flooring is not an expense. It's a property improvement.
The new flooring is entered the assets/depreciation section with an "in service" date of the closing date of your sale and a business use percentage of ZERO since the property was never rented out after that new flooring was installed.
