The correct option is
A much
In the given sentence, the word 'too' indicates an extreme degree of quantity of 'furniture'. Thus, the answer must complete the adjective of quantity and indicate an extreme degree, and since, 'too' already indicates an extreme degree, the answer must be in its positive degree.
Option A is correct. 'much' is an adjective of quantity which, when paired with 'too', indicates an extreme degree. Thus, it is the correct answer.
Option B is incorrect. 'more' is in its comparative degree. Since, there is no comparison between two objects, 'more' is the incorrect answer
Option C is incorrect. 'many' is used to describe plural and countable noun. Here, 'furniture' is an uncountable and singular noun. Thus, 'many' is the incorrect answer.
Option D is incorrect. 'most' is in its superlative degree form. Since, 'too' is already present to indicate an extreme degree, 'most' is the incorrect answer.