Paul,

Whether you do or do not purchase a subwoofer, a question to ask is:

How do recordings that you like sound on your current monitoring system? Do they also sound too bass heavy or bass-light?

Until you answer that question, the matter of purchase of a subwoofer should be delayed in my opinion.

If your reference recordings sound fine, and they also sound enjoyable to your ear on your home hi-fi system, whilst your own recordings may sound fine on your monitoring system, but seem too bass heavy or bass weak on your hi-fi with a sub, then you can begin the process of purchase of a subwoofer and the effort that goes along with it to properly cross-over content being fed to it vs. your KRKs.

Mixing while sitting in a corner is not normally recommended - that's where you will have the most low frequency room modes interacting. You MIGHT make the situation worse by adding a subwoofer. In most home studios (read: smaller spaces, bedrooms, even closets, etc.), the room cavity modes normally play a very large role interacting with your mixing location.

It's also really difficult to make the room mode interaction 'go away'. In other words, room acoustics play a large role here that should not be ignored in your decision.

You might consider forgoing a new subwoofer and using a local thrift shop purchase for it. You likely can nearly knock a zero off of the price. See if you can tune the cross-over frequency such that you make your reference recording sound properly balanced. Then proceed to your own mixing activities.

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