consider the risk of ruin, or disaster stop (something happens outside the market, terrorism, major news or you lose connection and ability to exit).
because even if you have stops in place and a major news event happens, your stop will blow and big time at that.
that's the major loss you need to focus on. it's rare, but when it happens it can end your trading career.
therefore calculate your number of contracts using this disaster loss. choose the maximum number of contracts you can accept that loss with.
regarding the psychological aspect of increasing :
remove those $ P/L from your screen.
think in terms of ticks only. then size won't matter (since you chose a size that won't ruin you).
if you are profitable with 2, you will be with 5. just make sure you don't look at the dollars.