Simply put: Not necessarily.
“Firmness” is often mistaken for “support”, and the two are hardly related. Firmness simply refers to the feel of the mattress – how hard or soft it is. Support refers to the design or construction and whether it promotes proper spine and neck alignment, which is crucial for good sleep. Both are important – you won’t sleep well on a mattress that you don’t think is comfortable (firmness). Likewise, a mattress that feels comfortable at first won’t offer great sleep if it isn’t supportive.
There is no right or wrong answer here; you’ll sleep best on what you think is comfortable. However, there are some points to keep in mind.
An extra firm mattress may not have enough give to contour to the shape of your body. This will cause pressure points, which cut off circulation, which causes you to toss and turn (often unknowingly), which results in not getting a good night’s sleep. An extra soft mattress may have the opposite effect, causing you to sink into a “puddle” and not giving enough support to keep your spine and neck aligned.
To sleep comfortably, find just the right balance of support and cushioning that feels right for you.
Whether you like firm or soft, if you want better sleep it is crucial to pick a mattress with proper support. If you like the feel of a coil spring mattress best, look for one with individually wrapped coils. If you prefer foam, the higher density foams typically offer the best support.
There are virtually endless combinations of coils and foam that can be combined for both comfort and support. Price isn’t necessarily indicative of quality – speak to a salesperson who is knowledgeable enough to explain the pros and cons of each mattress and who can help you select the perfect one for you, regardless of its price tag.