Learning to strop is key to maintenance. Don’t worry about convexing the edge. Yes there may be some convexing of the bevel, but it is a good thing.

The slight Convexing will never prevent the edge from shaving, because you are polishing the whole bevel equally, not just the edge.

Rolling the edge is from lifting the spine or too much downward pressure, common with a paddle strop or with a pasted strop. A pasted strop is an abrasive strop and just one mis-stroke can wipe an edge.

Learn stropping technique, the stropping muscle memory on a nylon strop and once comfortable go to a good leather strop. You can buy a good strop for well under 40 dollars. An expensive strop will not give you better edge until you improve your technique.

Finding a local mentor will increase your learning curve with some hands-on coaching.