Will using two condoms be better protection from pregnancy and STIs?

Two condoms are definitely NOT better than one. Two condoms can create more friction, which increases the chances the condom(s) will break.
If you want to be super safe, use a condom and an effective contraceptive method.
Try a different method: implant

References:

1. World Health Organization Department of Reproductive Health and Research and Johns Hopkins Bloomberg School of Public Health Center for Communication Programs (2018) Family Planning: A Global Handbook for Providers. Baltimore and Geneva. Retrieved from https://apps.who.int/iris/bitstream/handle/10665/260156/9780999203705-eng.pdf?sequence=1