I have made the cattle panel trellises but lean 8' plastic coated poles toward each other to make an upside-down V. But lately I've been buying trellis netting from online nurseries in like 50' lengths and stringing it on plastic-coated wire between heavy T-posts so I have more area. This year I bought some plastic trellis from Johnny's that is very cheap- $58 for 250', 6.5' tall, but the holes in the trellis are 6.5" and now that I have it I think that is a little large as it makes kind of big spaces between plants. I will probably end up with more that one vine per strand. I also don't know how many years I will get out of it. The trellis netting is made of nylon and has held up several years so far.

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It's quite common on low sites where I live. The latin term for it is "Arundinaria gigantea". The link below is the only place I know of that sells it. Here is a link that might be useful: BambooSourcery

It's going to do poorly until it gets better light. Also, you shouldn't have pruned it as the leaves would have come back if it had more light. Bamboo does not regenerate branches or culms that are lopped off, so that stub is going to continue to look like that, although it should put out some leaves if you can improve the lighting. Bamboo can be grown indoors, but not easily, and there are some bamboo that can tolerate lower light than the one you have, so are better candidates for indoors. The advantage of the species you have (presumably Phyllostachys nigra?) is that it can survive down to about -10C in a pot (-15C in the ground). It also likes water, and, as long as it's in a pot with drainage, a lot or rain won't hurt it. I live in the Seattle area where it's rainy, windy, and gray out for 4-5 of the winter months, and Belgium is probably no worse. I have a lot of bamboo species in the ground and at least a dozen different ones in pots, and they all stay leafy throughout the winter. I think you are actually hurting your plant by keeping it inside, rather than protecting it. If you set it outside, it may not re-leaf much until it gets warmer, but I think it will be happier. The only downside is that severe, constant winds could cause leaf burn in the winter, but shouldn't otherwise damage the plant. The only thing that will hurt it in your climate is if the temperatures go below the ones I mentioned above. However, if it does get really cold, you could always bring the pot in for a day or two until the cold snap passes.