Well there are many documents and academical research from porminent sources stating that forced Islamization has not been evident during the Ottoman Empire, to the contrary most monesteries and churches were actually build in Bulgarian during Ottoman Turkish rule. The Ottoman Millet based system allowed freedom of religon and wide freedoms for it subjects with the main prerequisite being that taxes are paid on time. Adoption of Islam for personal benefit or other reasons has been voluntary and in Bulgaria involed mainly the higher nobility class (matter of convinience).
Islamic missionaries were active in Bulgaria already durig the 9th century, also mentioned in a letter by the Pope at that time. Pomak is a reference to a ethnic group inhabiting the area of the Rhodopes for a millenia...the origin of the Pomaks has been investigated down to DNA level and are quite far from the current ethnic Bulgarian population. And no the Pomaks did not sell their religion and kept their language and No the Gagauz did not sell their language and kept their religion (Buglarian mumbo jumbo ala State Security historical department)
BTW Proto-Bulgarians have not left much traces on the current Bulgarian population, who are completely Slavisized with no cultural or linguistic links to the Turkic Proto-Bulgarians. Thracians are Bulgarian? no wonder Bulgarian history is such a mess, you write it as you go.
Pomaks