I think the reason that BAF is waiting to decide on new single engine fighter (a bit of topic for this thread), is because the existing choices are all a couple of decades (at least a decade) old. This is a crucial time where 5th Gen. aircraft are coming online (with extensive redesign for having stealth profile) and 4th Gen. aircraft will rapidly become obsolete.
As a result, 4th gen. aircraft (if they are still being produced) will not demand premium pricing, which may be a boon to Bangladesh Air Force (for now, 4th gen. can be usable for at least one more decade).
These below are the 5th Gen. small fighter programs, some are already flying.
Shenyang J-31 (F-60) – China
This fighter aircraft by China is currently under progress by Shenyang Aircraft Corporation and
first flew in 2012. The aircraft is also popularly known by the names Falcon Hawk, F-60 or J-21 Snowy Owl, Gyrfalcon, etc. This may or may not be offered for export.
7. TAI TFX / F-X – Turkey
Turkey has started its work in the development of its personal fifth generation aircraft known as TFX by the Turkish Aerospace Industries (TAI).
Still on paper.
6. Mitsubishi ATD-X (Shinshin) – Japan
Currently flying. Japan committed in the development of fifth generation fighter aircraft known as ATD-X (Shinshin). This aircraft uses the stealth technology which is being developed for the research purposes by Ministry of Defense Technical Research and Development Institute (TRDI). Considered as the first domestic stealth fighter from Japan
5. KAI KF-X – South Korea
KAI KF-X is being developed for the Republic of Korea Air Force (ROKAF) and Indonesian Air Force (TNI-AU). Still on paper but progressing rapidly. Indonesia is investing 20% in project. There are two versions it seems. C100 and C200.
Still on paper.
6. Mikoyan LMFS - Russia
This is the successor to the Mig-35's role in stealth redesign (LMFS stands for Liogkiy Mnogofunktsionalniy Frontovoi Samolyet — or Light Multi-Function Frontal Aircraft). Still in very initial stages of design. Went through many design changes and will go through a couple more it seems.
Still on paper.
I intentionally left out Indian JV's with Russia but the LMFS might be in that category. BAF will not make any purchases from India, that we can be certain. And F-35 is wayyyy to expensive for BAF (way overkill and skills to operate does not currently exist).
Here is a rough idea of size for some of these.