Whether to switch depends a lot on how much you're earning and how many clients you have. If you're consistently over 5k euros a month, it's worth seriously looking into standard VAT because with the flat rate you're paying tax on your entire turnover anyway (after the flat-rate deduction), whereas with VAT you can deduct what you pay on expenses and materials. But heads up: with standard VAT you've got more bureaucratic obligations, you have to issue VAT invoices, file VAT returns quarterly or monthly, and your accountant will cost you more than it does now. It's not a decision you make on the fly.
Your accountant can calculate the real benefit using your exact numbers: the cost of the tax structure (accountant included), the expenses you can deduct, your overall tax burden. I'd read through the quote they gave you and ask them in writing exactly how much you'd save monthly by making the switch. There's also another thing to consider: are you sure you'll keep earning at this level? If it's just a temporary phase, switching might not be worth it. But if it's stable and growing, then yeah, going for standard VAT makes sense.
One thing people often overlook: with the flat rate you're "simple" to manage and attract less attention, while standard VAT puts your numbers more on display. It's not a bad thing, but it's extra bureaucratic stress. Talk to your accountant again and get them to put together a comparison document, not just their opinions. And anyway if you decide to switch, do it from the start of the fiscal year - it's less of a headache.