Search is not about keywords. It is about whole language.
There are several factors at play when someone searches for your site besides the content. For now, I will stick to your question directly.
Search is about linguistic semantics. In your case, handmade or custom would be a modifier of curtains. The term curtains would be the most important term with any modifier you use second. Both modifiers apply so you should probably use both. The two terms, handmade and custom, are not synonymous but have unique meanings.
The comma is of no consequence except to list the modifiers. From a purely semantics perspective, the comma indicates that you are listing modifiers to curtains. Even without the comma, the two modifiers will still apply. Grammatically and linguistically speaking, using the comma is correct.
Be natural in the use of your language. People are who you are targeting and not machines. Search engines understand your content better than you can imagine. Linguistic analysis was around in the 1950's and used by computer systems in the 1970's. Since then the use of linguistics has really grown up though though the foundation has been well established for decades.
Next, you want to use the language of your target audience. You do not say what country you are targeting so I will assume the U.S. for illustration.
The term bespoke is not a commonly used term. It may be in other countries of course. Think about how your target audience would search for your site speaking into a smartphone. One way to know this is to ask a few friends to find what you offer by speaking into a smartphone. Listen to what the say or ask. This is key.
I have for decades emplored people to use natural language in their content. Why? Because people use natural language in searching the internet. Semantics relies upon natural language. Take the searches you have gathered from your friends and answer the question or search. Do not jam in what you think you should, but rather, what others think you should. Are you getting my drift?
Lastly, there are many other factors besides your content that is extremely important in search. For example, Google My Business, schema.org mark-up, fully semantic inbound links, navigational links, domain name branded or otherwise, URL, proper use of the title tag, meta description tag, h1 tag, and any other header tag. Create content that is very traditional. Create content with full sentences where you can. For navigational links, make sure they are fully semantic including subject and modifier or subject, predicate and object. For example, "custom curtains", and "In home solutions for London".
Once you create your content, think about your audience over and over again and fine tune your content for people. Add to that all of the other points I suggested. You want Google to find your "business" more than your "content".