KTM 390 Adventure

Since you are used to a good amount of performance, we'd suggest you move to something like the Triumph Speed 400. This bike will meet your needs of having a comfortable riding position as well as a reasonably low seat height. 

There are more comfortable options available, but almost all of them are adventure bikes with relatively tall seats. If you can get along with a taller seat, we'd recommend options like the Royal Enfield Himalayan 450 or KTM 390 Adventure as good replacements for your Aprilia RS 457. 

Adventure bikes are a great option for a one bike garage when you need to do long trips, especially at the lower end of the market. We would advise you to pick between the Royal Enfield Himalayan 450 and the KTM 390 Adventure duo, depending on your needs. Both options have great comfort, strong performance and superb comfort, so take a long test ride to see which one suits you best. 

If you want your new bike to be sporty and compact, then bikes like the KTM 390 Duke, TVS Apache RTR 310 and Honda CB300R would be our recommendation. 

If you want to have a machine that's capable of doing longer distances with luggage and/or a pillion, then an adventure bike like the KTM 390 Adventure (either of the 2 variants will do) or the Royal Enfield Himalayan 450 will fit the bill. 

Before pulling the trigger, try to get long test rides of every bike you are considering to make an informed decision.