Straw Is No Problem.Availability of straw would be a big consideration also?
Our market doesn't mind either slats or straw, the only bonus to slats is that it is less work when cleaning. Could we get away with slats without ventilation or is it a probelm?Your building and your market will decide for you!
If you don't have proper insulation and control of your ventilation then straw will help, 7kg piglets in a draughty shed without some form of bedding will be carnage.
If it's contract rearing then the end market will most likely specify what you must use.
If you want to do it efficiently then temperature controlled buildings on slats is usually best.
Lots of "ifs"!