Learn Finnish: Uusi huonekalumme on kallis. - Our new piece of furniture is expensive.

It is made of the noun huonekalu (piece of furniture) and the first-person plural possessive suffix -mme (our). Together they mean "our piece of furniture".

Should I use the word meidän (our) in this sentence?

You can say meidän uusi huonekalumme, but it isn't strictly necessary in standard or written Finnish. The suffix -mme already tells us whose furniture it is. Keep in mind that in casual spoken Finnish, people usually do the opposite: they say meidän uusi huonekalu and drop the suffix entirely!

Why doesn't the adjective uusi get a matching suffix?

Possessive suffixes are only attached to the noun, never to the adjectives that describe it. The adjective just stays in its normal form. This is why it is uusi huonekalumme and not uusimme huonekalumme.

Is huonekalu a compound word?

Yes! It literally translates to "room tool" or "room item", combining huone (room) and kalu (tool, object).