Get a growbag, loosen the compost and bounce it down to two thirds it original length, fold the flap under, put it on the floor in the greenhouse and flatten the top a bit. Cut the bottom out of the biggest pot you have which is just smaller than the width of the growbag. Put the bottomless pot on the growbag and cut a hole in the growbag, the same size as the pot, then shove the pot in and push in a cane. Take your tomato plant carefully out of its pot and put it in the pot in the growbag. Backfill the new pot with compost until it reaches the first true leaf joint. Water it in.
The plant won't know it's been moved. A growbag will take 2 toms.
Hope this helps.

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