You are wrong in thinking that it rules out willows. I have to do root influence calculations regularly as part of my job (landscape architect).
Firstly, willows and any other trees are unlikely to crack a pipe. All roots start as tiny threads that grow through the gaps in the soil, they do not possess jackhammers to make their own cracks. If the pipework is sound, then they will not penetrate it. It is true that once they have grown through a pre-existing crack they will eventually thicken causing damage. However, in your case...
The next thing to consider is that the influence on foundations tends to be related to the effects on soil shrinkage. During the summer, a large tree can remove a large quantity of water from the soil. If it is a high shrinkage soil (such as clay), this will cause it shrink. In winter, when they shed their leaves and rain saturates the soil it will expand again. Over time this will cause heaving of the soil. The amount of shrinkage a particular tree or shrub will cause is in part related to their water demand and in part due to their total leaf area (i.e. the bit that gets rid of the water). In the case of willows, they are high water demand trees, meaning that you would need to site them further from foundations than many other trees of the same size. In your case, limiting their height to 3m would mean you should be safe to plant them 6-8m from foundations. Limiting their height will also limit the distance their roots grow thus reducing the risk of invading damaged pipework.
You do not want an overly vigorous cultivar as you will forever be pruning it and your structure will become woody and end up being rather short lived. You do want something that is going to be pliable and not branch too much. It is worth contacting a supplier of living willow and discussing the details of your project with them. I disagree with one of the posts that says willows like humid conditions. Admittedly, some do, but not all. Salix are highly diverse and can be found in habitats ranging from deserts through to tundra (both of which are not at all humid!). Salix exigua might be a good candidate it is hardy in the UK, very beautiful and drought tolerant.
Another answer mentions hazel. I haven't seen it used before for this purpose, however, it does produce quite pliable straight rods in the first year after coppicing. It is slower growing and is a low water demand species. It does not strike readily from cuttings though, so you would need to plant plants rather than rods as this case for willow.
See NHBC root guidelines