The way a 35mm SLR worked is still pretty much the same concept now minus the sensor or film area. Whilst before you could shoot direct to IR film, DSLRs have an IR filter to stop causing issues with the final image.   This cannot be removed easily since it's there to serve a very fundamental purpose and by removing it, could lead to poor quality photos or if not done carefully, damage to components or the sensor itself.   The digital and cheapest fix is going to use IR filters but cause havoc with shutter speeds and focusing so you either go down the tripod route or really bump up the ISO but in turn, lowering the quality of images.   The most straight forward option would be to just use a 35mm SLR. There are specialists who maybe able to provide a conversion but voids any warranty but will also mean you DLR will only be able to take IR photos which is why the filters came about.   Hope that gives you some insight.