For Samatha-first as a basis for insight practices, I highly recommend Ajaan Lee's freely available manual 'Keeping the Breath in Mind,' specifically method 2. For even more, check out Thanissaro Bhikkhu's 'With Each and Every Breath.' The Thai Forest Samatha approach is excellent imho.
Then for more to build onto that, and especially to use it as a basis for insight, check out Rob Burbea's concentration/samatha/jhana retreats on DharmaSeed:
https://dharmaseed.org/retreats/4496/
https://dharmaseed.org/retreats/1183/
Rob Burbea was a long-term student of Thanissaro Bhikkhu, so his approach is more or less based upon the Thai Forest Samatha approach, and he goes in-depth into using it as a basis for deep insights, especially into emptiness which is sort of his speciality.
