To bring them indoors while flowering and green leafed as I see in your photo would spell disaster as far as the Lilly bulb getting recharged and getting the proper amount of down time for next growing season; it will never get enough sun for bulb development nor cool temperatures required for dormancy inside your home.

I was going to put it back outside in the cold greenhouse once the flowers had finished to die down.

Bringing some of the garden inside the house. Yes my wife used to do that to decorate the guest rooms when visitors came to stay for a few days.

Try not to have it in a warm room if you try bringing it in though or it might suffer from the shock of the change. And it will be shocked again when you put it outside.

You could try cutting the flower stems and bringing those in instead?

Good idea Steragram, Thank You :o))

Enjoy!