^^^ What he said. Chair flying is the best training you can do, and it's free. Think of it as an actor learning lines. So much of flying is scans, flows and memory items it needs to be second nature.
With regards to apps - if you are doing an IR course, you'll have a competent instructor and probably more hours in the SIM than you need. To put it into context, I flew VFR for my first 1500 hours, and I ABSOLUTELY KNEW that IFR flying was a black art, the hardest thing you can do, and that I would be all the help I could get. So I bought a brand new top spec gaming PC, X plane, yoke and pedals. Imagine my disbelief after about 6 hours in the SIM, my instructor told me that we had covered everything I needed to know and the rest is just practice! He was complaining because the course was just too long. I still haven't taken that PC out of the box. So trust me, unless you're spreading the IR over a year, the SIM time should be enough.