Great question and welcome to the Forum. It’s always assumed everyone has lots of space and wants / needs more colonies.
To reduce the likelihood of swarming it’s the standard stuff around keeping younger queens, having less swarmy strains of queens, providing space ahead of their needs, swapping brood from over strong colonies to weaker ones, regular inspections to spot queen cells etc. However, bees swarm as a natural part of their reproductive cycle so swarming is also an expression of them doing well, so will be attempted at some stage. As a starter I would just concentrate on giving them enough space and regular inspections for queen cells.
Maybe your question is how if they try to swarm (ie start queen cells), do I stop them leaving without buying more hives? What many of us do is still make splits but do it vertically on the same hive stand. You can look up various splits online (Snelgrove, Snelgrove II, Demaree, Pagden) but most are based on version of separating the queen and brood. That way, all you need is an extra brood box with frames and an extra crown board to its feed holes blocked off and a notch cut out the rim to act as a entrance - known as a split board.
You do your swarm split but the artificial swarm box instead of being to one side just goes on the top of your existing hive stack, split board with entrance slot 90 degrees to the normal entrance and the new brood box over that. Simples.
Minimal extra kit, and effective. Once they have settled down, they are on the same stack so easy to unite hack. You can do other things but more options are not always helpful! I currently use the Snelgrove II method described by Wally Shaw, as its reliable and simple. Hope that helps.