For the combination of best rates and very low cost debit card convenience, I cannot recommend the TransferWise 'Borderless' card highly enough. (https://transferwise.com/gb/borderless/card).
Living on the continent (France & then Spain) but with a UK account & pension, I found out years ago that Transferwise was the best outfit to transfer one currency to another.
More recently, they started a system called a 'borderless' account, which allows you to hold a balance with them in a number of currencies, should you wish. This comes with a Mastercard debit card that can be used wherever they take Mastercard and is perfect for taking on holiday. You can get cash at local ATMs, spend in shops, hotels & restaurants & all with much lower fees than almost anyone else in the market.
It is a prepaid card, so is probably not best used for car-hire deposits, but you can simply do a bank transfer to your Transferwise account in pounds before you leave. It's all automatic and you can always top it up on your bank app or Internet banking whilst you're away. If you want to save even more, and/or protect your budget against currency fluctuations, you can transfer some of your money into your desired currency in advance. Spending in that currency then gets no further charges.
As with most cards, it's never a good idea to allow the merchant to charge you in Pounds. The rate they use is invariably a rip-off & you're already getting the best rate possible through TransferWise.
Sorry if this sounds like an ad for TransferWise. I've been using them for over ten years and have used my debit card in Spain, the US, Dubai & Switzerland & it works a treat.