Additions to the flock after death?

On Sunday my 'baby' of the flock died after having been ill for almost two years. In her life she needed a lot of extra care and often lived inside the home with us when she just couldn't cope outside. Sometimes we'd bring her inside when she was just so ill we wanted to giver her a comfortable end and she managed to pull through, other times because the other chickens knew she was the weakest and naturally pecked at her or didn't let her have enough food. We'd bring her in and sort her out within an hour and she'd be fine again.

For the last three weeks of her life Casserole was inside. Whilst the other two hens own health improved without her for a long period of time (Casserole had been ill since birth but it still seemed to rub off on the others). However we also noticed they seemed kind of lonely. They haven't been as playful without their other friend bouncing along at their side and exploring the garden.

I've read that hens are naturally happiest in groups of three or more, but because of things like school and work, we wouldn't be able to get a new hen until at June. We couldn't keep an eye on it and ensure it was settling in properly because nobody would be around to do so.

So my question is, is it worth buying another hen in June, given they'll have had a few months to getting used to being a duo rather than a trio, or should I leave them as a pair, at least until they are back to their normal selves?

How have other people dealt with this situation?