TX Estate Planners: Need Your Help inre Account Titles

I'm trying to open a brokerage account for my wife & I that ultimately avoids probate and receives a 100% step-up in cost basis at the time of death.

TD Ameritrade has suggested that I open one of the following: Joint Tenants (with Rights of Survivorship), or a Community Property account.

My understanding is that a Joint Tenant account avoids probate, but only 50% of the assets experience a step-up in cost basis at the time of death. A Community Property account would receive a 100% step-up in cost basis at the time of death, but 50% of the account would wind up in the deceased's estate. Is it possible to avoid that by attaching a Survivorship agreement to the account, or should I subject the account to probate and have my will designate her as the beneficiary?

Bigger picture, does account titling even really matter in a community property state? Aren't all assets (excluding gifts and inheritance) accumulated after the date of marriage considered community property?

TIA