Quilt 450

Take a look at Rab neutrino 400, or consider cumulus quilt 450 with some sort of down hood and/or down/climashield apex socks. Thermarest xtherm pad is great.

You could have a look at Cumulus. I've been happy with their 450 quilt.

I think you can cheap out on most pieces of gear, but for me the sleeping bag/quilt would be the one item I would spend some money on. I prefer a down quilt since it generally packs a little smaller and is more versatile in different temperature ranges. Down is expensive, but I hear good things about Decathlon's lightweight down bags. Otherwise I would recommend looking at Cumulus for a European produced quilt. For May-September in Europe I would recommend a comfort rating of about 0°C, which is what I use almost all year round. Make sure when you are buying the bag/quilt that you are actually looking for the comfort rating, and not the "sleep limit" or "minimal" rating or whatever. Regarding the sleeping pad I think you will be fine with a foam pad as long as you find a way to attach it to your bike. If you decide to invest in an inflatable pad I would recommend to look for something that's packable and has an R value of about 3.

I'm comfortable in my (Cumulus) quilt right down to the comfort temp they give in the same stuff I'd sleep in a bag except something on my head. I think it's more lack of standardization.

I recommend a quilt from Cumulus. I have one for bikepacking - I move a lot when I sleep (swapping between side/stomach/back), and quilt is the only way to go. Cumulus is great quality, made in the EU, fast delivery, small pack size.

Take a look at cumulus bags. They can do custom fill (up or down, “waterproof” different fabrics etc ) and custom sizing for it as well if you wish. Not cheap but personally I think they’re the best down bags on the market.