Problem with multiple shipping dimensions in the UK

[EmmaSeren]

Hi

I'm having a nightmare with shipping. I sell handmade dolls of various sizes and doll clothes to customers all over the world. I'm a very small business and only have a basic profile and can't afford to pay for any of the shipping apps. 

The problem I am having is this. 

My larger dolls are sent in a box as a parcel via Royal Mail

My smaller dolls are sent in an envelope as a parcel via Royal Mail

My doll clothes are sent in an envelope as a large letter via Royal Mail

Many customers buy multiple dolls and will often buy dolls and clothes together. 

So far I have had to come up with a crazy work-around system using the weight based profiles to account for the different package sizes and costs....

I input all clothes as weighing 10g and charge a large letter rate for anything under 200g

I pretend my smaller dolls weigh 200g and charge a parcel rate for them

I pretend my bigger dolls weigh 300g and charge a higher parcel rate for them

My logic is that this way a customer can buy quite a few clothes without triggering a parcel price of shipping. 

This crazy system is by no means ideal, but it has meant I've been able to use Shopify for the last few years. 

I've just designed a tiny doll baby. It only weighs 10g in real life and can be sent in small envelope, but because it is over 2.5cm thick Royal Mail will charge a parcel rate for it. Now when I've tried to include this in my crazy system to get around Shopify not allowing me to include dimensions it has broken my system. I have listed the babies as weighing 200g which will trigger the parcel rate. The problem is that lots of my customers have tried to buy multiple babies which has triggered really high shipping rates! They have also tried to buy them together with bigger dolls which again triggers a really shipping rate! 

I've thought about trying to offer a discount code so that if you buy more than one baby it only charges a certain amount of shipping, but you can't do that - you can only offer free shipping. 

I've thought about having a custom shipping rate for the babies, but then shopify just adds that the normal shipping rate if someone buys a baby and a doll, again resulting in a really high shipping cost. 

Is there any way around this problem? I've been trying to find an answer for years and find it incredible that shopify hasn't allowed us to include something so basic and fundamental to our shipping profiles! Can developers add it to my shop? 

Thanks

Emma