There's an important distinction here between companies that require you to work from home, and companies that allow it.
If your company has made home-working mandatory, even if not full-time (for example if you can only come into the office for a few days per week), in Sweden this entitles you to a safe working environment, both physically and mentally. The general rule is that the more you're expected to work from home, the greater your employer's responsibility to ensure a good working environment there.
You should have already been made aware of how your employer will do this, but if not, it's not too late to raise it. As an employee, you have the responsibility to inform your employer of any risks in your working environment, which includes things like an unsuitable desk or chair.
In other cases, your company might be allowing employees to return to the workplace but keeping home-working as an option.
If this is the case, you still have the right to a safe working environment while working from home, but when it's a perk rather than an obligation it's harder to negotiate. Your manager isn't obligated to approve all your requests and if they would be difficult for your employer to carry out, they might simply ask you to work from your usual workplace.
However, you can also make the point that it's more cost-effective for your employer to provide you with, say, a desk chair or computer screen now than to risk bearing the costs of lost working hours if you suffer injuries due to the lack of proper equipment.
Exactly what's covered by the right to a safe working environment isn't defined by law.
But it is generally understood to include ergonomic seating equipment (a desk and chair) for a desk-based job, appropriate lighting, and any equipment needed to allow you to use your computer safely, such as a laptop stand or wrist rest. It would also cover things like a computer, mobile phone, and internet connection, if required for your job.
Your employer might allow you to borrow these items from the office while working remotely, give you a budget to buy your own items, or ask you to submit individual requests for each item.
If your employer makes a contribution towards an item that you buy for yourself (rather than an item that you get to use at home but which belongs to the company), it counts as a taxable benefit. You may still prefer this option if you would like to keep the item after your employment ends, but it's worth bearing in mind.
It's possible that despite your best efforts, your environment at home won't reach the same standards as at the office. For example, many offices in Sweden offer standing desks for staff, and it may not be practical or possible to provide these for home-workers. If that's the case, you might need more frequent breaks to avoid injury or eye strain, for example.
And the safe working environment also covers mental health, so you should have defined working hours so that you can disconnect from work even if working from your home, and good communications with your manager and colleagues. This might mean scheduled daily catch-ups to replace the impromptu discussions you'd have at an office.
The best thing to do is to communicate clearly with your manager about what you think you need in order to carry out your work at home.