Prayer Process For A Person With Limited Mobility
In any worship ritual, including namaz, when there’s any undue difficulty (usar), then whatever the closest form that can be performed should be undertaken. In the case that you described above, the decision lies with the individual. If they feel comfortable standing then they can offer their namaz standing and make the sujood while sitting in a chair. On the other hand if they find it difficult to stand, they can offer the entire namaz while sitting in a chair. Even if they want to stand for a bit and then continue the rest while sitting down, that’s also acceptable. The key thing is that the person himself should decide knowing that in the matters of religion, God doesn’t want to burden anyone more than what they can bear.