It is possible to go without a sump. My tank has been running for 4 years without a sump and I know of many others who have the same setup.
I use a Juwel Filter that came with the tank, and have recently replaced the original juwel skimmer (sits on the inside of the tank) to a Deltec MCE 600 that hangs on the outside. No real risk of overflowing; the skimmercup has a pipe that returns any overskimmed water into the skimmer. Very satisfied with the deltec compared to juwel's skimmer, and gives more space in the tank!
I have read of some who use Eheim filters that sit outside of the tank, while others reccomend against those kinds of filters for saltwater aquariums. Maybe you can have a closer look into that and see if it could be an option. Some people put those filters in a tub in case of leaking; it gives you some extra time. There are also easy solutions to stop the flow if your tank gets below a certain water level. That way you could have a bucket that could fill up to a certain level if it leaks, and then stopping the filter completely when the tank water level is lowered to your decided point. No water on the floor!