which lifters to get?

I would be very surprised if the cam or springs caused the lifter to collapse. It may have been a defective lifter to start with or maybe the pre-load was to much. Hopefully it was not a wiped cam lobe. You don't have to replace them all, just the one that collapsed. Check your pre-loads when you reassemble the valve train. You may have to shim the rocker shafts if the pre-load is to much.

Jack