Is there a way to limit both weight and price on orders going to certain countries?
For example orders going to the EU over £135 (EUR150) are exempt from the IOSS and therefore can provide a poorer customer experience if they then get charged import duties etc. Also our shipping provider has limits on parcel weights that can be sent internationally.
With Shopify rates, you can only add one condition type or the other (weigh-based or price-based). You can't have both in the same profile/zone.
If you're open to using a third-party solution, Intuitive Shipping lets you set up Scenarios with multiple conditions that must all be met in order for a shipping method to be activated. For your requirement, you could have a Scenario just for EU countries with a price condition (cart total is less than or equals 135) and a weight condition (cart weight is less than or equals [carrier limit]). Then, set up your shipping method with the carrier costs and only assign it to an EU Zone.
If you're entering your carrier rates manually, you could even simplify this by only having the price condition in the Scenario. Then, in your shipping method -- which, again, would be assigned to the EU, build a shipping rate table based on weight. Any weights that exceed the highest limit in the table will not return a shipping cost to the customer.
Intuitive Shipping is free to use in Setup & Testing mode, so if you're interested in trying it out, you can install the app for free, set up the Scenario and run some test calculations without having to select a billing plan. This will allow you to see if it's a good fit for your store.
Please note that to use Intuitive Shipping - or any third-party rate calculation app - Shopify requires that you enable their third-party carrier-calculated shipping rates feature. This feature is $20 USD per month. If you change your Shopify billing to annual, they will add the feature at no additional cost (plus they will reduce your billing plan by 10%). If you're on the Advanced plan or higher, this feature is already included and activated by default.