I was aware that I would probably not be able to send or receive from non segwit addresses, but I decided to go for this option anyway, since I heard they are more efficient, so I preferred them over the "transitional" P2SH addresses.
My question is, will I be able to send/receive coins between my bech32 P2WPKH, and the P2SH addresses?
The thing is that segwit adoption is taking a lot of time, so I'm afraid that the "transitional" P2SH addresses get more "popular", and it will take a while for me to be able to really use my bech32 P2WPKH addresses.
Bech32-type addresses are more efficient, yes.
But you don't have any problems with sending/receiving to/from any address.
You can send/receive to/from any address you wish. Everything will work as before.
The problem with the slow adoption is that some wallets/exchanges/service provider won't allow you to enter a BTC address starting with bc1..
simply because they have a check-function to make sure you enter a "valid" btc address.
And as soon they check your address is neither starting with 1.. nor with 3.. they will give you an "wrong format" error.
This is just a problem of the exchanges/wallets/...
This has nothing to do with bitcoin/segwit itself.