Back in roman times they would use a sponge on a stick. Probably don't do that.
Just experiment with how few sheets you can use of your own loo roll without anything sneaking through. As for how many times to wipe you've just got to keep going until you're done. Depends on the poop.
You could use wet wipes, or dampen the loo roll. You could even use a bidet (but that would probably involve a whole bunch of new pluming) or if you're really desperate to shower your bum crack a sports top bottle. Just be aware that a lot of wet wipes aren't good to flush because they don't break down and can block pipes or harm the environment.
If you're concerned about wasting paper in the environmental sense you can get recycled or bamboo loo roll which are less wasteful.