[Sony Ericsson Xperia Mini, Mini Pro, Xperia Pro, A] OdlG26:
So I flashed WT19i_4.1.B.0.587_Generic Firmware with the Flashtool64. Worked fine just like that. Phone runs smooth now. Would still like to upgrade to Kitkat or Lollipop if possible. Bootloader unlock is still not allowed.

03/026/2015 16:26:11 - INFO - Flashtool Version 0.9.18.4 built on 12-05-2014 22:00:00
03/026/2015 16:26:11 - INFO - Executing search strategies to find proxy selector
03/026/2015 16:26:11 - INFO - No proxy found for IE. Trying next one
03/026/2015 16:26:11 - INFO - Strategy firefox failed trying next one : No Firefox installation found
03/026/2015 16:26:11 - INFO - No proxy found for java. Trying next one
03/026/2015 16:26:11 - INFO - Syncing devices from github
03/026/2015 16:26:12 - INFO - Scanning devices folder for changes.
03/026/2015 16:26:20 - INFO - Pulling changes from github.
03/026/2015 16:26:21 - INFO - Devices sync finished.
03/026/2015 16:26:25 - INFO - Device disconnected
03/026/2015 16:26:49 - INFO - Device connected with USB debugging on
03/026/2015 16:26:50 - INFO - Connected device : SonyEricson Xperia Live Walkman
03/026/2015 16:26:50 - INFO - Installed version of busybox : BusyBox v1.22.1-Stericson (2014-01-25 17:27:18 CET) multi-call binary.
03/026/2015 16:26:50 - INFO - Android version : 2.3.4 / kernel version : 2.6.32.9-perf / Build number : 4.0.2.A.0.62
03/026/2015 16:26:50 - INFO - Checking root access
03/026/2015 16:26:50 - INFO - Root Access Allowed
03/027/2015 16:27:04 - INFO - Selected Bundle for SonyEricson Xperia Live Walkman (WT19i). FW release : 4.1.B.0.587. Customization : Generic
03/027/2015 16:27:04 - INFO - Preparing files for flashing
03/027/2015 16:27:06 - INFO - Please connect your device into flashmode.
03/027/2015 16:27:11 - INFO - Device disconnected
03/027/2015 16:27:53 - INFO - Device connected in flash mode
03/027/2015 16:27:53 - INFO - Opening device for R/W
03/027/2015 16:27:53 - INFO - Reading device information
03/027/2015 16:27:54 - INFO - Phone ready for flashmode operations.
03/027/2015 16:27:54 - INFO - Current device : WT19i - BX902UW490 - 1262-9352_R1D - 1250-5829_4.0.2.A.0.62 - WORLD-i_4.0.2.A.0.62
03/027/2015 16:27:54 - INFO - Start Flashing
03/027/2015 16:27:54 - INFO - Processing loader.sin
03/027/2015 16:27:54 - INFO - Checking header
03/027/2015 16:27:54 - INFO - Flashing data
03/027/2015 16:27:54 - INFO - Processing of loader.sin finished.
03/027/2015 16:27:55 - INFO - Loader : S1_Loader_Root_773f - Version : R4A066 / Boot version : R9B031 / Bootloader status : NOT_ROOTABLE
03/027/2015 16:27:55 - INFO - No bootdelivery to send
03/027/2015 16:27:55 - INFO - Processing kernel.sin
03/027/2015 16:27:55 - INFO - Checking header
03/027/2015 16:27:55 - INFO - Flashing data
03/027/2015 16:27:57 - INFO - Processing of kernel.sin finished.
03/027/2015 16:27:57 - INFO - Processing fota0.sin
03/027/2015 16:27:57 - INFO - Checking header
03/027/2015 16:27:57 - INFO - Flashing data
03/027/2015 16:27:58 - INFO - Processing of fota0.sin finished.
03/027/2015 16:27:58 - INFO - Processing fota1.sin
03/027/2015 16:27:58 - INFO - Checking header
03/027/2015 16:27:58 - INFO - Flashing data
03/027/2015 16:27:59 - INFO - Processing of fota1.sin finished.
03/027/2015 16:27:59 - INFO - Processing adsp.sin
03/027/2015 16:27:59 - INFO - Checking header
03/027/2015 16:27:59 - INFO - Flashing data
03/028/2015 16:28:01 - INFO - Processing of adsp.sin finished.
03/028/2015 16:28:01 - INFO - Processing amss.sin
03/028/2015 16:28:01 - INFO - Checking header
03/028/2015 16:28:01 - INFO - Flashing data
03/028/2015 16:28:09 - INFO - Processing of amss.sin finished.
03/028/2015 16:28:09 - INFO - Processing amss_fs_coconut.sin
03/028/2015 16:28:09 - INFO - Checking header
03/028/2015 16:28:09 - INFO - Flashing data
03/028/2015 16:28:09 - INFO - Processing of amss_fs_coconut.sin finished.
03/028/2015 16:28:09 - INFO - Processing apps_log.sin
03/028/2015 16:28:09 - INFO - Checking header
03/028/2015 16:28:09 - INFO - Flashing data
03/028/2015 16:28:09 - INFO - Processing of apps_log.sin finished.
03/028/2015 16:28:09 - INFO - Processing cache.sin
03/028/2015 16:28:09 - INFO - Checking header
03/028/2015 16:28:09 - INFO - Flashing data
03/028/2015 16:28:10 - INFO - Processing of cache.sin finished.
03/028/2015 16:28:10 - INFO - Processing system.sin
03/028/2015 16:28:10 - INFO - Checking header
03/028/2015 16:28:10 - INFO - Flashing data
03/030/2015 16:30:40 - INFO - Processing of system.sin finished.
03/030/2015 16:30:40 - INFO - Processing userdata.sin
03/030/2015 16:30:40 - INFO - Checking header
03/030/2015 16:30:40 - INFO - Flashing data
03/030/2015 16:30:45 - INFO - Processing of userdata.sin finished.
03/030/2015 16:30:45 - WARN - This file is ignored : simlock.ta
03/030/2015 16:30:45 - INFO - Ending flash session
03/030/2015 16:30:45 - INFO - Flashing finished.
03/030/2015 16:30:45 - INFO - Please unplug and start your phone
03/030/2015 16:30:45 - INFO - For flashtool, Unknown Sources and Debugging must be checked in phone settings
03/030/2015 16:30:45 - INFO - Device connected in flash mode
03/030/2015 16:30:55 - INFO - Device disconnected